A156541 Multiplicative closure of Sophie Germain primes (A005384).

1, 2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 15, 16, 18, 20, 22, 23, 24, 25, 27, 29, 30, 32, 33, 36, 40, 41, 44, 45, 46, 48, 50, 53, 54, 55, 58, 60, 64, 66, 69, 72, 75, 80, 81, 82, 83, 87, 88, 89, 90, 92, 96, 99, 100, 106, 108, 110, 113, 115, 116, 120, 121, 123, 125, 128, 131, 132

Offset

1,2

Comments

A156542(a(n)) = A001221(a(n));

Subsequence of A130176.

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

Maple

q:= n-> andmap(p-> isprime(2*p+1), ifactors(n)[2][.., 1]):
select(q, [$1..132])[];  # Alois P. Heinz, Nov 25 2025

Mathematica

Select[Range@132, And @@ PrimeQ[FactorInteger[#][[All, 1]]*2 + 1] &] (* Ivan Neretin, Aug 30 2015 *)

Crossrefs

Cf. A156541, A156543.

Sequence in context: A332487 A067942 A130176 * A325663 A277620 A031143

Adjacent sequences: A156538 A156539 A156540 * A156542 A156543 A156544

Keyword

nonn

Author

Reinhard Zumkeller, Feb 10 2009

Status

approved