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A073255 Sum of divisors of n-th composite number. 17
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
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
Sequence in context: A341092 A351474 A349854 * A162194 A247954 A145310
KEYWORD
nonn
AUTHOR
Labos Elemer, Jul 22 2002
STATUS
approved

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Last modified March 29 08:01 EDT 2024. Contains 371265 sequences. (Running on oeis4.)