A247787 Sum of divisors of 2*prime(n)-1.

4, 6, 13, 14, 32, 31, 48, 38, 78, 80, 62, 74, 121, 108, 128, 192, 182, 133, 160, 192, 180, 158, 288, 240, 194, 272, 252, 288, 256, 403, 288, 390, 448, 278, 480, 352, 314, 434, 494, 576, 576, 381, 512, 576, 528, 398, 422, 540, 608, 458, 768, 702, 532, 672

Offset: 1

Author

Jaroslav Krizek, Sep 24 2014

Keywords

• nonn
• easy

Comments

See A005382 (primes p such that sigma(2p-1) = 2p).

Examples

			For n = 3; prime(3) = 5, a(3) = sigma(2*5-1) = sigma(9) = 13.
		

Links

• Jens Kruse Andersen, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000203, A072057, A005382, A247788.

Programs

Magma

[SumOfDivisors(2*p-1): p in PrimesUpTo(2000)]

PARI

vector(100,n,sigma(2*prime(n)-1)) \\ Derek Orr, Sep 25 2014

Formula

a(n) = sigma(A076274(n)) = A000203(A076274(n)).