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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.)