A247954 a(n) = sigma(sigma(2n-1)).

1, 7, 12, 15, 14, 28, 24, 60, 39, 42, 63, 60, 32, 90, 72, 63, 124, 124, 60, 120, 96, 84, 168, 124, 80, 195, 120, 195, 186, 168, 96, 210, 224, 126, 252, 195, 114, 224, 252, 186, 133, 224, 280, 360, 234, 248, 255, 360, 171, 392, 216, 210, 508, 280, 216, 300

Offset: 1

Author

Jaroslav Krizek, Sep 28 2014

Keywords

• nonn
• easy

Comments

See A247821 - numbers k such that sigma(sigma(2k-1)) is a prime p.

Examples

			For n=2; a(2) = sigma(sigma(2*2-1)) = sigma(sigma(3)) = sigma(4) = 7.
		

Links

• Indranil Ghosh, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000203, A051027, A008438, A247820.

Programs

Magma

[SumOfDivisors(SumOfDivisors(2*n-1)): n in [1..1000]];

Maple

with(numtheory): A247954:=n->sigma(sigma(2*n-1)): seq(A247954(n), n=1..50); # Wesley Ivan Hurt, Oct 01 2014

Mathematica

Table[DivisorSigma[1, DivisorSigma[1, 2 n - 1]], {n, 50}] (* Wesley Ivan Hurt, Oct 01 2014 *)

PARI

vector(100,n,sigma(sigma(2*n-1))) \\ Derek Orr, Sep 29 2014

Formula

a(n) = A000203(A000203(2n-1)) = A000203(A008438(n-1)) = A051027(2n-1).