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A147810 Half the number of divisors of n^2+1. +0
4
1, 1, 2, 1, 2, 1, 3, 2, 2, 1, 2, 2, 4, 1, 2, 1, 4, 3, 2, 1, 4, 2, 4, 1, 2, 1, 4, 2, 2, 2, 4, 3, 4, 2, 2, 1, 4, 3, 2, 1, 3, 2, 6, 2, 2, 2, 8, 2, 2, 2, 2, 2, 4, 1, 4, 1, 8, 2, 2, 2, 2, 2, 4, 2, 2, 1, 4, 4, 2, 3, 2, 4, 8, 1, 4, 2, 4, 2, 2, 2, 4, 3, 8, 1, 2, 2, 4, 2, 4, 1, 4, 2, 6, 1, 2, 2, 4, 4, 6 (list; graph; listen)
OFFSET

1,3

COMMENT

For any n>0, n^2+1 cannot be a square and thus has an even number of divisors which always include 1 and n^2+1, therefore a(n) is always a positive integer.

FORMULA

a(n) = A000005(A002522(n))/2 = A147809(n)+1

PROGRAM

(PARI) A147810(n)=numdiv(n^2+1)/2

CROSSREFS

Cf. A048691.

Sequence in context: A059829 A076558 A057217 this_sequence A055181 A073811 A125030

Adjacent sequences: A147807 A147808 A147809 this_sequence A147811 A147812 A147813

KEYWORD

easy,nonn

AUTHOR

M. F. Hasler (MHasler(AT)univ-ag.fr), Dec 13 2008

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Last modified November 27 22:38 EST 2009. Contains 167602 sequences.


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