A224081 Numbers k such that A112141(k) + 1 is prime.

1, 4, 5, 6, 11, 12, 18, 39, 51, 98, 124, 170, 179, 208, 248, 838, 919, 939, 1233, 1352, 2177, 3070, 10714

Offset

1,2

Comments

This is the semiprime analog to A014545.

Links

Table of n, a(n) for n=1..23.

Example

4*6*9*10+1 = 2161 which is prime.

Mathematica

NextSemiPrime[n_, k_: 1] := Block[{c = 0, sgn = Sign[k]}, sp = n + sgn; While[c < Abs[k], While[ PrimeOmega[sp] != 2, If[sgn < 0, sp--, sp++]]; If[sgn < 0, sp--, sp++]; c++]; sp + If[sgn < 0, 1, -1]]; f[n_] := Times @@ NestList[NextSemiPrime, 2^2, n - 1]; k = 1; lst = {}; While[k < 4651, If[ PrimeQ[f[k] + 1], Print[k]; AppendTo[lst, k]]; k++]; lst

Crossrefs

Cf. A112141, A014545, A224082.

Sequence in context: A007606 A284513 A047311 * A347269 A316783 A076138

Adjacent sequences: A224078 A224079 A224080 * A224082 A224083 A224084

Keyword

nonn,more

Author

Jonathan Vos Post and Robert G. Wilson v, Apr 02 2013

Extensions

a(23) from Tyler Busby, Feb 12 2023

Status

approved