A006197 Least number not dividing binomial(2n,n).

3, 4, 3, 3, 5, 5, 5, 4, 3, 3, 5, 3, 3, 7, 7, 4, 7, 8, 9, 8, 7, 7, 7, 7, 5, 5, 3, 3, 9, 3, 3, 4, 8, 8, 5, 3, 3, 9, 3, 3, 13, 13, 13, 11, 11, 11, 11, 8, 7, 5, 5, 5, 13, 9, 5, 5, 5, 7, 7, 5, 5, 5, 7, 4, 7, 7, 9, 8, 13, 7, 7

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

Comments

All terms are prime powers (A246655). [Corrected by Amiram Eldar, May 27 2024]

References

• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• T. D. Noe, Table of n, a(n) for n=1..10000
• P. Erdős, R. L. Graham, I. Z. Russa and E. G. Straus, On the prime factors of C(2n,n), Math. Comp. 29 (1975), 83-92.

Crossrefs

Cf. A000984, A007978, A246655.

Programs

Mathematica

a[n_] := Module[{k = 1, b = Binomial[2*n, n]}, While[Divisible[b, k], k++]; k]; Array[a, 100] (* Amiram Eldar, May 27 2024 *)

Formula

a(n) = A007978(A000984(n)). - Amiram Eldar, May 27 2024