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A188172
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Number of divisors d of n of the form d == 7 (mod 8).
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7
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0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 1, 2, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1
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OFFSET
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1,63
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COMMENTS
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a(A188226(n))=n and a(m)<>n for m<A188226(n), n>=0; a(A141164(n))=1. - Reinhard Zumkeller, Mar 26 2011
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LINKS
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_Reinhard Zumkeller_, Table of n, a(n) for n = 1..10000
M. D. Hirschhorn, The number of representations of a number by various forms, Discrete Mathematics 298 (2005), 205-211.
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FORMULA
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A188170(n)+a(n) = A001842(n).
A188169(n)+A188170(n)-A188171(n)-a(n) = A002325(n).
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EXAMPLE
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a(A007522(i)) = 1, any i.
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MAPLE
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sigmamr := proc(n, m, r) local a, d ; a := 0 ; for d in numtheory[divisors](n) do if modp(d, m) = r then a := a+1 ; end if; end do: a; end proc:
A188172 := proc(n) sigmamr(n, 8, 7) ; end proc:
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PROG
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(Haskell)
a188172 n = length $ filter ((== 0) . mod n) [7, 15..n]
-- Reinhard Zumkeller, Mar 26 2011
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CROSSREFS
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Cf. A004771.
Sequence in context: A083895 A093488 A085858 * A106671 A033776 A117371
Adjacent sequences: A188169 A188170 A188171 * A188173 A188174 A188175
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KEYWORD
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nonn,easy
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AUTHOR
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R. J. Mathar, Mar 23 2011
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STATUS
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approved
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