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A001826
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Number of divisors of n of form 4k+1.
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9
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1, 1, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 2, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 1, 3, 2, 2, 1, 2, 2, 1, 1, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 1, 1, 4, 1, 1, 1, 2, 3, 2, 2, 2, 2, 2, 1, 2, 2, 1, 2, 2, 1, 3, 1, 4, 2, 1, 2, 2, 2, 1, 2, 2, 2, 3, 1, 2, 2, 1, 2, 3, 2, 1, 2, 4, 1, 2, 1, 2, 4, 2, 1, 2, 1, 2, 1, 2, 2, 3, 3, 2, 2, 1, 2, 4
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,5
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LINKS
| Nick Hobson, Table of n, a(n) for n = 1..10000
Michael Gilleland, Some Self-Similar Integer Sequences
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FORMULA
| G.f.: Sum_{n>0} x^n/(1-x^(4n)) = Sum x^(4n+1)/(1-x^(4n+1)), n=0..inf.
a(n) = A001227(n) - A001842(n). - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Apr 18 2006
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MAPLE
| d:=proc(r, m, n) local i, t1; t1:=0; for i from 1 to n do if n mod i = 0 and i-r mod m = 0 then t1:=t1+1; fi; od: t1; end; # no. of divisors i of n with i == r mod m
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PROG
| (PARI) a(n)=if(n<1, 0, sumdiv(n, d, d%4==1))
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CROSSREFS
| Sequence in context: A046951 A159631 A050377 * A003641 A165190 A025890
Adjacent sequences: A001823 A001824 A001825 * A001827 A001828 A001829
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| Better definition from Michael Somos, Apr 26 2004
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