A089643 - OEIS

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A089643

3^a(n) divides C(3n,n); 3-adic valuation of A005809.

0, 1, 1, 1, 2, 1, 1, 2, 2, 1, 2, 2, 2, 3, 1, 1, 2, 2, 1, 2, 2, 2, 3, 2, 2, 3, 3, 1, 2, 2, 2, 3, 2, 2, 3, 3, 2, 3, 3, 3, 4, 1, 1, 2, 2, 1, 2, 2, 2, 3, 2, 2, 3, 3, 1, 2, 2, 2, 3, 2, 2, 3, 3, 2, 3, 3, 3, 4, 2, 2, 3, 3, 2, 3, 3, 3, 4, 3, 3, 4, 4, 1, 2, 2, 2, 3, 2, 2, 3, 3, 2, 3, 3, 3, 4, 2, 2, 3, 3, 2, 3, 3, 3, 4, 3

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OFFSET

0,5

LINKS

Antti Karttunen, Table of n, a(n) for n = 0..19683

FORMULA

a(n) = A007949(A005809(n)). - Antti Karttunen, Jul 29 2017

a(n) = A054861(3*n) - A054861(2*n) - A054861(n). - David A. Corneth, Jul 29 2017

a(n) = A053735(2*n)/2. - Amiram Eldar, Feb 21 2021

MATHEMATICA

Table[IntegerExponent[Binomial[3 n, n], 3], {n, 0, 104}] (* Michael De Vlieger, Jul 29 2017 *)

PROG