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A161841 Number of factors, with repetition, in all distinct pairs (a <= b) such that a*b = n. 7
2, 2, 2, 4, 2, 4, 2, 4, 4, 4, 2, 6, 2, 4, 4, 6, 2, 6, 2, 6, 4, 4, 2, 8, 4, 4, 4, 6, 2, 8, 2, 6, 4, 4, 4, 10, 2, 4, 4, 8, 2, 8, 2, 6, 6, 4, 2, 10, 4, 6, 4, 6, 2, 8, 4, 8, 4, 4, 2, 12, 2, 4, 6, 8, 4, 8, 2, 6, 4, 8, 2, 12, 2, 4, 6, 6, 4, 8, 2, 10, 6, 4, 2, 12, 4, 4, 4, 8, 2, 12, 4, 6, 4, 4, 4, 12, 2, 6, 6, 10 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A000005(n) + A010052(n) = A038548(n)*2.

Sum_{k=1..n} a(k) ~ (log(n) + 2*gamma - 1)*n + sqrt(n), where gamma is the Euler-Mascheroni constant A001620. - Vaclav Kotesovec, Jul 01 2021

EXAMPLE

a(16)=6 because there are three distinct pairs (a <= b) such that a*b = n: the pairs (1,16), (2,8) and (4,4). So the number of factors, with repetition, in all the pairs is equal to 6.

MAPLE

seq(numtheory:-tau(n) + `if`(issqr(n), 1, 0), n = 1 .. 200); # Robert Israel, Dec 23 2015

CROSSREFS

Cf. A000005, A010052, A038548, A161842.

Sequence in context: A332347 A201353 A072048 * A335901 A152674 A072056

Adjacent sequences: A161838 A161839 A161840 * A161842 A161843 A161844

KEYWORD

easy,nonn

AUTHOR

Omar E. Pol, Jun 23 2009

STATUS

approved

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Last modified November 30 17:37 EST 2022. Contains 358453 sequences. (Running on oeis4.)