A278230 Least number with the prime signature of 2*prime(n) + 1.

2, 2, 2, 6, 2, 8, 6, 6, 2, 2, 12, 12, 2, 6, 6, 2, 6, 6, 24, 6, 12, 6, 2, 2, 30, 6, 12, 6, 6, 2, 30, 2, 12, 12, 6, 6, 60, 6, 6, 2, 2, 12, 2, 12, 6, 30, 12, 6, 30, 24, 2, 2, 30, 2, 6, 6, 12, 6, 30, 2, 48, 2, 30, 6, 30, 6, 30, 72, 6, 6, 6, 2, 60, 12, 30, 6, 6, 30, 6, 60, 2, 6, 2, 12, 6, 2, 6, 30, 6, 12, 30, 6, 60, 2, 24, 6, 2, 6, 6, 12, 30, 6, 12, 6, 12, 210, 12

Offset: 1

Author

Antti Karttunen, Nov 19 2016

Keywords

• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000040, A046523, A072055.

Cf. A072192 (positions of 2's), A005384.

Cf. also A278227, A278228, A278229.

Programs

Mathematica

Table[Times @@ MapIndexed[(Prime@ First@ #2)^#1 &, #] &@ If[Length@ # == 1 && #[[1, 1]] == 1, {0}, Reverse@ Sort@ #[[All, -1]]] &@ FactorInteger[ 2 Prime@ n + 1], {n, 120}] (* Michael De Vlieger, Nov 21 2016 *)

Scheme

(define (A278230 n) (A046523 (+ 1 (* 2 (A000040 n)))))

Formula

a(n) = A046523(A072055(n)) = A046523(1 + 2*A000040(n)).