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A051027 a(n) = sigma(sigma(n)) = sum of the divisors of the sum of the divisors of n. 51
1, 4, 7, 8, 12, 28, 15, 24, 14, 39, 28, 56, 24, 60, 60, 32, 39, 56, 42, 96, 63, 91, 60, 168, 32, 96, 90, 120, 72, 195, 63, 104, 124, 120, 124, 112, 60, 168, 120, 234, 96, 252, 84, 224, 168, 195, 124, 224, 80, 128, 195, 171, 120, 360, 195, 360, 186, 234, 168, 480, 96 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

If n is prime, a(n) = sigma(n+1) = A000203(n+1). - Wesley Ivan Hurt, Feb 14 2014

LINKS

T. D. Noe, Table of n, a(n) for n=1..5000

FORMULA

a(n)=A000203(A000203(n)). [Zak Seidov, Aug 29 2012]

EXAMPLE

a(2)=4 because sigma(2)=1+2=3 and sigma(3)=1+3=4. [Zak Seidov, Aug 29 2012]

MAPLE

with(numtheory): [seq(sigma(sigma(n)), n=1..100)];

MATHEMATICA

DivisorSigma[1, DivisorSigma[1, Range[100]]] (* Zak Seidov, Aug 29 2012 *)

PROG

(PARI) a(n)=sigma(sigma(n)); \\ Joerg Arndt, Feb 16 2014

CROSSREFS

Cf. A000203.

Sequence in context: A070286 A047536 A093494 * A073435 A086987 A051219

Adjacent sequences:  A051024 A051025 A051026 * A051028 A051029 A051030

KEYWORD

easy,nice,nonn,look

AUTHOR

Judson D. Neer (judson(AT)poboxes.com)

STATUS

approved

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Last modified July 27 04:25 EDT 2017. Contains 289841 sequences.