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A073255 Sum of divisors of n-th composite number. 12
7, 12, 15, 13, 18, 28, 24, 24, 31, 39, 42, 32, 36, 60, 31, 42, 40, 56, 72, 63, 48, 54, 48, 91, 60, 56, 90, 96, 84, 78, 72, 124, 57, 93, 72, 98, 120, 72, 120, 80, 90, 168, 96, 104, 127, 84, 144, 126, 96, 144, 195, 114, 124, 140, 96, 168, 186, 121, 126, 224, 108, 132 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A000203(A002808(n)).

EXAMPLE

First composite is 4, sigma[4]=1+2+4=7=a(1).

MAPLE

map(numtheory:-sigma, remove(isprime, [$4..100])); # Robert Israel, Aug 27 2018

MATHEMATICA

c[x_] := FixedPoint[x+PrimePi[ # ]+1&, x] Table[DivisorSigma[1, c[w]], {w, 1, 128}]

DivisorSigma[1, #]&/@(Select[Range[100], CompositeQ]) (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Mar 10 2019 *)

PROG

(PARI) lista(nn) = forcomposite(c=1, nn, print1(sigma(c), ", ")); \\ Michel Marcus, Feb 21 2016

CROSSREFS

Cf. A000203, A002808, A035004.

Sequence in context: A317670 A062730 A287562 * A162194 A247954 A145310

Adjacent sequences:  A073252 A073253 A073254 * A073256 A073257 A073258

KEYWORD

nonn

AUTHOR

Labos Elemer, Jul 22 2002

STATUS

approved

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Last modified January 23 10:48 EST 2020. Contains 331171 sequences. (Running on oeis4.)