A072056 Number of divisors of 2*prime(n)+1.

2, 2, 2, 4, 2, 4, 4, 4, 2, 2, 6, 6, 2, 4, 4, 2, 4, 4, 8, 4, 6, 4, 2, 2, 8, 4, 6, 4, 4, 2, 8, 2, 6, 6, 4, 4, 12, 4, 4, 2, 2, 6, 2, 6, 4, 8, 6, 4, 8, 8, 2, 2, 8, 2, 4, 4, 6, 4, 8, 2, 10, 2, 8, 4, 8, 4, 8, 12, 4, 4, 4, 2, 12, 6, 8, 4, 4, 8, 4, 12, 2, 4, 2, 6, 4, 2, 4, 8, 4, 6, 8, 4, 12

Offset: 1

Author

Reinhard Zumkeller, Jun 11 2002

Keywords

• nonn

Examples

			Divisors of A072055(8) = 2*A000040(8)+1 = 2*19+1=39: {1,3,13,39} with size 4, therefore a(8) = 4.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000005, A000040, A072055, A072057.

Programs

Mathematica

Table[DivisorSigma[0,2Prime[n]+1],{n,100}] (* Harvey P. Dale, Apr 12 2021 *)

PARI

a(n) = numdiv(2*prime(n)+1); \\ Amiram Eldar, Apr 26 2024

PARI

lista(pmax) = forprime(p = 2, pmax, print1(numdiv(2*p+1), ", ")); \\ Amiram Eldar, Apr 26 2024

Formula

a(n) = A000005(A072055(n)).