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A259673
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a(n) = sigma_(prime(n))(n).
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2
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1, 9, 244, 16513, 48828126, 13062296532, 232630513987208, 144115462954287105, 8862938119746644274757, 100000000186264514923632574038, 191943424957750480504146841291812, 8505622499882988712256991112913772434548, 4695452425098908797088971409337422035076128814
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = [x^n] Sum_{k>=1} k^prime(n)*x^k/(1 - x^k). - Ilya Gutkovskiy, Sep 26 2017
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MAPLE
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a:= n-> numtheory[sigma][ithprime(n)](n):
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MATHEMATICA
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a[n_] := DivisorSigma[Prime[n], n]; Array[a, 13]
(* Second program: *)
a[n_] := SeriesCoefficient[Sum[k^Prime[n]*x^k/(1-x^k), {k, 1, n}], {x, 0, n}]; Array[a, 13] (* Jean-François Alcover, Sep 29 2017, from 2nd formula *)
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PROG
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(Magma) [DivisorSigma(NthPrime(n), n):n in [1..15]]; // Vincenzo Librandi, Jul 15 2015
(Python)
from sympy import divisor_sigma, prime
....return divisor_sigma(n, prime(n)) # Chai Wah Wu, Jul 20 2015
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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