This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A080225 Number of perfect divisors of n. 7
 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,84 COMMENTS Number of divisors d of n with sigma(d)=2*d (sigma=A000203); A080224(n)+a(n)+A080226(n)=A000005(n). LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 Eric Weisstein's World of Mathematics, Perfect Number. Wikipedia, Perfect number EXAMPLE Divisors of n=84: {1,2,3,4,6,7,12,14,21,24,28,42}, two of them are perfect: 6=A000396(1) and 28=A000396(2), therefore a(84)=2. PROG (Haskell) a080225 n = length [d | d <- takeWhile (<= n) a000396_list, mod n d == 0] -- Reinhard Zumkeller, Jan 20 2012 CROSSREFS Cf. A000396, A000203, A147645. Sequence in context: A317576 A070205 A138363 * A122841 A060862 A325801 Adjacent sequences:  A080222 A080223 A080224 * A080226 A080227 A080228 KEYWORD nonn AUTHOR Reinhard Zumkeller, Feb 07 2003 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified June 20 08:06 EDT 2019. Contains 324229 sequences. (Running on oeis4.)