A174217 a(n) = (A174216(n)-1)/2.

7, 13, 31, 61, 139, 283, 571, 1153, 2311, 4723, 9463, 19141, 38569, 77419, 154873, 310231, 620911, 1241923, 2483869, 4967803, 9946273, 19892599

Offset: 1

Author

Vladimir Shevelev, Mar 12 2010

Keywords

• nonn
• more

Comments

Related to the generation of twin primes according to section 6 of the preprint.

Links

• V. Shevelev, Theorems on twin primes-dual case, arXiv:0912.4006 [math.GM], 2009-2014.

Crossrefs

Cf. A174214, A174215, A174216, A166945, A167495.

Programs

Mathematica

(* b = A174214 *) b[n_] := b[n] = Which[n == 9, 14, CoprimeQ[b[n - 1], n - 1 - (-1)^n], b[n - 1] + 1, True, 2 n - 4];
(* c = A174216 *) c[n_] := c[n] = If[n == 1, 15, For[k = c[n - 1] + 1, True, k++, If[2 b[k] == 3 (k - 1), Return[k]]]];
Table[a[n] = (c[n] - 1)/2; Print["a(", n, ") = ", a[n]]; a[n], {n, 1, 22}] (* Jean-François Alcover, Jan 29 2019 *)

Formula

A174214(A174216(n)) = 3*a(n), n>1.

Extensions

Terms after a(11) corrected by Vladimir Shevelev, Nov 02 2010