OFFSET
1,2
COMMENTS
See A247821 - numbers n such that sigma(sigma(2n-1)) is a prime p.
LINKS
Indranil Ghosh, Table of n, a(n) for n = 1..10000
EXAMPLE
For n=2; a(2) = sigma(sigma(2*2-1)) = sigma(sigma(3)) = sigma(4) = 7.
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 *)
PROG
(Magma) [SumOfDivisors(SumOfDivisors(2*n-1)): n in [1..1000]]
(PARI) vector(100, n, sigma(sigma(2*n-1))) \\ Derek Orr, Sep 29 2014
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jaroslav Krizek, Sep 28 2014
STATUS
approved