A264046 Numbers k such that k and k+6 are consecutive semiprimes.

15, 123, 365, 371, 505, 545, 573, 591, 649, 707, 807, 843, 943, 1067, 1159, 1247, 1357, 1405, 1529, 1555, 1633, 1739, 1745, 1829, 1843, 1897, 1909, 1985, 2149, 2159, 2209, 2285, 2329, 2353, 2363, 2407, 2413, 2463, 2501, 2643, 2773, 2779

Offset

1,1

Comments

Note that a(1) = 15 = A131109(k=6).

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Example

15 = A001358(6) and 21 = A001358(7).

Mathematica

Select[Partition[Select[Range[3000], PrimeOmega[#]==2&], 2, 1], #[[2]]-#[[1]]==6&][[;; , 1]] (* Harvey P. Dale, Dec 24 2023 *)

Prog

(PARI) is(n)=if(bigomega(n)!=2 || bigomega(n+6)!=2, return(0)); for(i=1, 5, if(bigomega(n+i)==2, return(0))); 1 \\ Charles R Greathouse IV, Nov 02 2015

Crossrefs

Cf. A001358, A065516, A123375, A131109, A136196, A264043, A264044, A264045.

Sequence in context: A264377 A038743 A181377 * A349295 A027839 A034271

Adjacent sequences: A264043 A264044 A264045 * A264047 A264048 A264049

Keyword

nonn

Author

Zak Seidov, Nov 02 2015

Status

approved