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A247954
a(n) = sigma(sigma(2n-1)).
8
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
1,2
COMMENTS
See A247821 - numbers n such that sigma(sigma(2n-1)) is a prime p.
LINKS
FORMULA
a(n) = A000203(A000203(2n-1)) = A000203(A008438(n-1)) = A051027(2n-1).
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