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A062249
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a(n) = n + d(n), where d(n) = number of divisors of n, cf. A000005.
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17
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2, 4, 5, 7, 7, 10, 9, 12, 12, 14, 13, 18, 15, 18, 19, 21, 19, 24, 21, 26, 25, 26, 25, 32, 28, 30, 31, 34, 31, 38, 33, 38, 37, 38, 39, 45, 39, 42, 43, 48, 43, 50, 45, 50, 51, 50, 49, 58, 52, 56, 55, 58, 55, 62, 59, 64, 61, 62, 61, 72, 63, 66, 69, 71, 69, 74, 69, 74, 73, 78, 73
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OFFSET
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1,1
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COMMENTS
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Number of cyclic subgroups of dihedral group with 2n elements.
a(n) is the n-th smallest number not a divisor of n. - J. Lowell, Apr 06 2008
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LINKS
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FORMULA
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G.f.: x/(1 - x)^2 + Sum_{k>=1} x^k/(1 - x^k).
Dirichlet g.f.: zeta(s)^2 + zeta(s-1). (End)
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MAPLE
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MATHEMATICA
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Table[n + DivisorSigma[0, n], {n, 100}] (* Indranil Ghosh, Apr 12 2017 *)
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PROG
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(Haskell)
(Python)
from sympy.ntheory import divisor_count
[n + divisor_count(n) for n in range(101)] # Indranil Ghosh, Apr 12 2017
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Ahmed Fares (ahmedfares(AT)my-deja.com), Jul 01 2001
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EXTENSIONS
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STATUS
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approved
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