Cuban primes
The task (k == 1)
Not the most efficient, but concise, and good enough for this task.
sub comma { $^i.flip.comb(3).join(',').flip }
my @cubans = lazy (1..Inf).hyper(:8degree).map({ ($_+1)³ - .³ }).grep: *.is-prime;
put @cubans[^200]».&comma».fmt("%9s").rotor(10).join: "\n";
put '';
put @cubans[99_999]., # zero indexed
Output:
7 19 37 61 127 271 331 397 547 631
919 1,657 1,801 1,951 2,269 2,437 2,791 3,169 3,571 4,219
4,447 5,167 5,419 6,211 7,057 7,351 8,269 9,241 10,267 11,719
12,097 13,267 13,669 16,651 19,441 19,927 22,447 23,497 24,571 25,117
26,227 27,361 33,391 35,317 42,841 45,757 47,251 49,537 50,311 55,897
59,221 60,919 65,269 70,687 73,477 74,419 75,367 81,181 82,171 87,211
88,237 89,269 92,401 96,661 102,121 103,231 104,347 110,017 112,327 114,661
115,837 126,691 129,169 131,671 135,469 140,617 144,541 145,861 151,201 155,269
163,567 169,219 170,647 176,419 180,811 189,757 200,467 202,021 213,067 231,019
234,361 241,117 246,247 251,431 260,191 263,737 267,307 276,337 279,991 283,669
285,517 292,969 296,731 298,621 310,087 329,677 333,667 337,681 347,821 351,919
360,187 368,551 372,769 374,887 377,011 383,419 387,721 398,581 407,377 423,001
436,627 452,797 459,817 476,407 478,801 493,291 522,919 527,941 553,411 574,219
584,767 590,077 592,741 595,411 603,457 608,851 611,557 619,711 627,919 650,071
658,477 666,937 689,761 692,641 698,419 707,131 733,591 742,519 760,537 769,627
772,669 784,897 791,047 812,761 825,301 837,937 847,477 863,497 879,667 886,177
895,987 909,151 915,769 925,741 929,077 932,419 939,121 952,597 972,991 976,411
986,707 990,151 997,057 1,021,417 1,024,921 1,035,469 1,074,607 1,085,407 1,110,817 1,114,471
1,125,469 1,155,061 1,177,507 1,181,269 1,215,397 1,253,887 1,281,187 1,285,111 1,324,681 1,328,671
1,372,957 1,409,731 1,422,097 1,426,231 1,442,827 1,451,161 1,480,519 1,484,737 1,527,247 1,570,357
1,792,617,147,127
k == 2 through 10
After reading up a bit, the general equation for cuban primes is prime numbers of the form ((x+k)3 - x3)/k where k mod 3 is not equal 0.
The cubans where k == 1 (the focus of this task) is one of many possible groups. In general, it seems like the cubans where k == 1 and k == 2 are the two primary cases, but it is possible to have cubans with a k of any integer that is not a multiple of 3.
Here are the first 20 for each valid k up to 10:
sub comma { $^i.flip.comb(3).join(',').flip }
for 2..10 -> \k {
next if k %% 3;
my @cubans = lazy (1..Inf).map({ (($_+k)³ - .³)/k }).grep: *.is-prime;
put "First 20 cuban primes where k = {k}:";
put @cubans[^20]».&comma».fmt("%7s").rotor(10).join: "\n";
put '';
}
Output:
First 20 cuban primes where k = 2:
13 109 193 433 769 1,201 1,453 2,029 3,469 3,889
4,801 10,093 12,289 13,873 18,253 20,173 21,169 22,189 28,813 37,633
First 20 cuban primes where k = 4:
31 79 151 367 1,087 1,327 1,879 2,887 3,271 4,111
4,567 6,079 7,207 8,431 15,991 16,879 17,791 19,687 23,767 24,847
First 20 cuban primes where k = 5:
43 67 97 223 277 337 727 823 1,033 1,663
2,113 2,617 2,797 3,373 4,003 5,683 6,217 7,963 10,273 10,627
First 20 cuban primes where k = 7:
73 103 139 181 229 283 409 643 733 829
1,039 1,153 1,399 1,531 1,669 2,281 2,803 3,181 3,583 3,793
First 20 cuban primes where k = 8:
163 379 523 691 883 2,203 2,539 3,691 5,059 5,563
6,091 7,219 8,443 9,091 10,459 11,923 15,139 19,699 24,859 27,091
First 20 cuban primes where k = 10:
457 613 997 1,753 2,053 2,377 4,357 6,373 9,433 13,093
16,453 21,193 27,673 28,837 31,237 37,657 46,153 47,653 49,177 62,233
k == 2^128
Note that Perl 6 has native support for arbitrarily large integers and does not need to generate primes to test for primality. Using k of 2^128; finishes in well under a second.
sub comma { $^i.flip.comb(3).join(',').flip }
my \k = 2**128;
put "First 10 cuban primes where k = {k}:";
.&comma.put for (lazy (0..Inf).map({ (($_+k)³ - .³)/k }).grep: *.is-prime)[^10];
Output:
First 10 cuban primes where k = 340282366920938463463374607431768211456:
115,792,089,237,316,195,423,570,985,008,687,908,160,544,961,995,247,996,546,884,854,518,799,824,856,507
115,792,089,237,316,195,423,570,985,008,687,908,174,836,821,405,927,412,012,346,588,030,934,089,763,531
115,792,089,237,316,195,423,570,985,008,687,908,219,754,093,839,491,289,189,512,036,211,927,493,764,691
115,792,089,237,316,195,423,570,985,008,687,908,383,089,629,961,541,751,651,931,847,779,176,235,685,011
115,792,089,237,316,195,423,570,985,008,687,908,491,299,422,642,400,183,033,284,972,942,478,527,291,811
115,792,089,237,316,195,423,570,985,008,687,908,771,011,528,251,411,600,000,178,900,251,391,998,361,371
115,792,089,237,316,195,423,570,985,008,687,908,875,137,932,529,218,769,819,971,530,125,513,071,648,307
115,792,089,237,316,195,423,570,985,008,687,908,956,805,700,590,244,001,051,181,435,909,137,442,897,427
115,792,089,237,316,195,423,570,985,008,687,909,028,264,997,643,641,078,378,490,103,469,808,767,771,907
115,792,089,237,316,195,423,570,985,008,687,909,158,933,426,541,281,448,348,425,952,723,607,761,904,131