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A000989 3-adic valuation of binomial(2n ,n): largest k such that 3^k divides binomial(2n ,n). 3
0, 0, 1, 0, 0, 2, 1, 1, 2, 0, 0, 1, 0, 0, 3, 2, 2, 3, 1, 1, 2, 1, 1, 3, 2, 2, 3, 0, 0, 1, 0, 0, 2, 1, 1, 2, 0, 0, 1, 0, 0, 4, 3, 3, 4, 2, 2, 3, 2, 2, 4, 3, 3, 4, 1, 1, 2, 1, 1, 3, 2, 2, 3, 1, 1, 2, 1, 1, 4, 3, 3, 4, 2, 2, 3, 2, 2, 4, 3, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,6

COMMENTS

a(n) = 0 if and only if n is in A005836. - Charles R Greathouse IV, May 19 2013

sign(a(n+1) - a(n)) is repeat [0, 1, -1]. - Filip Zaludek, Oct 29 2016

By Kummer's theorem, number of carries when adding n + n in base 3. - Robert Israel, Oct 30 2016

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..2000

Michael Gilleland, Some Self-Similar Integer Sequences

Wikipedia, Kummer's theorem

FORMULA

a(n) = Sum_{k>=0} floor(2*n/3^k) - 2*Sum_{k>=0} floor(n/3^k). - Benoit Cloitre, Aug 26 2003

a(n) = A007949(A000984(n)). - Reinhard Zumkeller, Nov 19 2015

From Robert Israel, Oct 30 2016: (Start)

If 2*n < 3^k then a(3^k+n) = a(n).

If n < 3^k < 2*n then a(3^k+n) = a(n)+1.

If n < 3^k then a(2*3^k+n) = a(n)+1. (End)

MAPLE

f:= proc(n) option remember; local k, m, d;

   k:= floor(log[3](n));

   d:= floor(n/3^k);

   m:= n-d*3^k;

   if d = 2 or 2*m > 3^k then procname(m)+1

   else procname(m)

   fi

end proc:

f(0):= 0:

map(f, [$0..100]); # Robert Israel, Oct 30 2016

MATHEMATICA

p=3; Array[ If[ Mod[ bi=Binomial[ 2#, # ], p ]==0, Select[ FactorInteger[ bi ], Function[ q, q[ [ 1 ] ]==p ], 1 ][ [ 1, 2 ] ], 0 ]&, 27*3, 0 ]

Table[ IntegerExponent[ Binomial[2 n, n], 3], {n, 0, 100}] (* Jean-Fran├žois Alcover, Feb 15 2016 *)

PROG

(PARI) a(n) = valuation(binomial(2*n, n), 3)

(PARI) a(n)=my(N=2*n, s); while(N\=3, s+=N); while(n\=3, s-=2*n); s \\ Charles R Greathouse IV, May 19 2013

(Haskell)

a000989 = a007949 . a000984  -- Reinhard Zumkeller, Nov 19 2015

CROSSREFS

Cf. A000984, A005836, A007949.

Sequence in context: A062979 A114781 A083890 * A132401 A104273 A051778

Adjacent sequences:  A000986 A000987 A000988 * A000990 A000991 A000992

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, R. K. Guy

STATUS

approved

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Last modified May 28 14:10 EDT 2017. Contains 287241 sequences.