A125770 First occurrence of in A125769.

1, 2, 7, 9, 34, 31, 54, 15, 16, 26, 148, 68, 398, 62, 193, 25, 27, 140, 550, 397, 107, 113, 50, 122, 950, 226, 38, 169, 40, 562, 187, 44, 327, 763, 70, 211, 362, 49, 1726, 79, 394, 153, 55, 202, 1600, 125, 61, 419, 94, 95, 225, 98, 66, 1036, 508, 1298, 983, 69, 71

Offset

1,2

Comments

If we restrict ourselves to just j*T_k +1 or j*T_k -1 then there are vaulues which do not occur. As an example if the minus is used then 8&9 are missing.

Links

Table of n, a(n) for n=1..59.

Mathematica

triQ[n_] := IntegerQ@ Sqrt[8*n + 1]; f[n_] := Block[{j = 1, p = Prime@n}, While[ !triQ[(p - 1)/j] && !triQ[(p + 1)/j], j++ ]; j]; t = Table[0, {100}]; Do[ a = f@n; If[a < 101 && t[[a]] == 0, t[[a]] = n; Print[{a, n}]], {n, 3500}]; t

Crossrefs

A125769 = a(n) is the least number j such that j*T_k +/- 1 is n-th prime for some k-th triangular number.

Cf. A000217, A125765, A125766, A125767, A125768, A125769.

Sequence in context: A319629 A033855 A126871 * A042063 A360734 A041717

Adjacent sequences: A125767 A125768 A125769 * A125771 A125772 A125773

Keyword

nonn

Author

Jonathan Vos Post & Robert G. Wilson v, Dec 03 2006

Status

approved