A126251 a(n) = (p+2)!/p! where p is the n-th lesser twin prime, A001359(n).

20, 42, 156, 342, 930, 1806, 3660, 5256, 10506, 11772, 19182, 22650, 32580, 37056, 39402, 52212, 57840, 73170, 79806, 97656, 121452, 176820, 187056, 213906, 273006, 325470, 360600, 382542, 412806, 436260, 656910, 676506, 686412, 737022, 778806

Offset: 1

Author

Zerinvary Lajos, Mar 08 2007

Keywords

• easy
• nonn

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A001359, A082669.

Subsequence of A002378.

Programs

Maple

ZL:=[]:for p from 1 to 1653 do if (isprime(p) and isprime(p+2)) then ZL:=[op(ZL),((p+2)!/p!)]; fi; od; print(ZL);

Mathematica

#[[2]]!/#[[1]]!&/@Select[Partition[Prime[Range[200]],2,1],#[[2]]-#[[1]] == 2&] (* Harvey P. Dale, Feb 16 2020 *)

Formula

a(n) = 2*A082669(n).

Extensions

Name edited by Michel Marcus, Apr 29 2023