id:A001826 - OEIS Search Results

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Number of divisors of n of form 4k+1.

+0
6

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; listen)

	OFFSET	`1,5`
	LINKS	`Nick Hobson, Table of n, a(n) for n = 1..10000` `Michael Gilleland, Some Self-Similar Integer Sequences`
	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`
	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`
	PROGRAM	`(PARI) a(n)=if(n<1, 0, sumdiv(n, d, d%4==1))`
	CROSSREFS	`Sequence in context: A046951 A159631 A050377 this_sequence A003641 A165190 A025890` `Adjacent sequences: A001823 A001824 A001825 this_sequence A001827 A001828 A001829`
	KEYWORD	`nonn`
	AUTHOR	`N. J. A. Sloane (njas(AT)research.att.com).`
	EXTENSIONS	`Better definition from Michael Somos, Apr 26 2004`

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Last modified November 23 17:09 EST 2009. Contains 167438 sequences.

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