A147810 - OEIS

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A147810

Half the number of divisors of n^2+1.

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; refs; listen; history; internal format)

	OFFSET	`1,3`
	COMMENTS	`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`
	PROG	`(PARI) A147810(n)=numdiv(n^2+1)/2`
	CROSSREFS	`Cf. A048691.` `Sequence in context: A204893 A057217 A193330 * A055181 A073811 A125030` `Adjacent sequences: A147807 A147808 A147809 * A147811 A147812 A147813`
	KEYWORD	`easy,nonn`
	AUTHOR	`M. F. Hasler (www.univ-ag.fr/~mhasler), Dec 13 2008`

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Last modified February 15 21:45 EST 2012. Contains 205860 sequences.