A109642 a(n) = least composite m such that binomial(3m,m) mod m = 3^n.

4, 15, 57, 765, 1025, 2097, 4947, 9189, 103599, 216927, 4346128, 1558269, 1977777, 208510373, 14493123, 493262541, 144228033

Offset: 1

Author

Ryan Propper, Aug 05 2005

Keywords

• nonn
• more

Comments

Subsequence of A109641.

Crossrefs

Cf. A080469, A109641.

Programs

Mathematica

In[1]:= n = 1; Do[If[ !PrimeQ[k] && Mod[Binomial[3*k, k], k] == 3^n, Print[k]; n++ ], {k, 1, 10^4}]

Extensions

Edited by Max Alekseyev, Nov 03 2009

a(14)-a(17) from Chai Wah Wu, Jul 30 2025