

A242627


Number of divisors of n that are less than 10.


22



9, 1, 2, 2, 3, 2, 4, 2, 4, 3, 3, 1, 5, 1, 3, 3, 4, 1, 5, 1, 4, 3, 2, 1, 6, 2, 2, 3, 4, 1, 5, 1, 4, 2, 2, 3, 6, 1, 2, 2, 5, 1, 5, 1, 3, 4, 2, 1, 6, 2, 3, 2, 3, 1, 5, 2, 5, 2, 2, 1, 6, 1, 2, 4, 4, 2, 4, 1, 3, 2, 4, 1, 7, 1, 2, 3, 3, 2, 4, 1, 5, 3, 2, 1, 6, 2
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OFFSET

0,1


COMMENTS

Number of numbers <= 9, dividing n;
a(n) <= 9; a(2520*n) = 9;
a(n) = (number of repdigit numbers in row n of triangle A242614) = sum(A202022(A242614(n,k)): k=1..A242622(n)), for n > 0.
Periodic with period 2520. Each period there are 576 1s, 720 2s, 464 3s, 360 4s, 206 5s, 122 6s, 58 7s, 13 8s, and 1 9 (average 2.82...).  Charles R Greathouse IV, Sep 27 2015


LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 0..10000
Index entries for linear recurrences with constant coefficients, signature (2,4,7,11,15,20,24,27,28,27,23,17,9,0,9,17,23,27,28,27,24,20,15,11,7,4,2,1).


FORMULA

G.f.: sum(j=1..9, 1/(1x^j)).  Robert Israel, Jul 31 2014


MAPLE

a:= n > numboccur(0, map2(`modp`, n, [$1..9])):
map(a, [$0..100]); # Robert Israel, Jul 31 2014


PROG

(Haskell)
a242627 n = length $ filter ((== 0) . mod n) [1..9]
(PARI) a(n)=1+sum(k=2, 9, n%k<1) \\ Zak Seidov, Jul 31 2014


CROSSREFS

Cf. A165412.
Sequence in context: A257437 A010166 A186116 * A289502 A010165 A177273
Adjacent sequences: A242624 A242625 A242626 * A242628 A242629 A242630


KEYWORD

nonn,easy


AUTHOR

Reinhard Zumkeller, Jul 16 2014


STATUS

approved



