

A129488


Smallest odd prime dividing binomial(2n,n).


4



3, 5, 5, 3, 3, 3, 3, 5, 11, 3, 7, 5, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 7, 5, 3, 7, 7, 3, 3, 3, 3, 7, 7, 3, 5, 5, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 5, 5, 3, 5, 5, 3, 3, 3, 3, 5, 5, 3, 5, 5, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3
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OFFSET

2,1


COMMENTS

The Erdős paper calls this function g(n) and states that it not known whether it is bounded. Currently, g(3160)=13 is the greatest known value of g. See A129489.


LINKS

T. D. Noe, Table of n, a(n) for n = 2..5000
P. Erdős, R. L. Graham, I. Z. Russa and E. G. Straus, On the prime factors of C(2n,n), Math. Comp. 29 (1975), 8392.


MATHEMATICA

Table[Transpose[FactorInteger[Binomial[2n, n]]][[1, 2]], {n, 2, 150}]


PROG

(PARI) a(n)=my(k); forprime(p=3, default(primelimit), k=1; while((k*=p)<=2*n, if(n/kn\k>1/2, return(p)))) \\ Charles R Greathouse IV, Dec 19 2011


CROSSREFS

Cf. A030979 (n such that g(n)>=11), A129489, A266366.
Sequence in context: A110551 A141334 A199614 * A211023 A279494 A053670
Adjacent sequences: A129485 A129486 A129487 * A129489 A129490 A129491


KEYWORD

nonn


AUTHOR

T. D. Noe, Apr 17 2007


STATUS

approved



