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 A109642 a(n) = least composite m such that binomial(3m,m) mod m = 3^n. 4
 4, 15, 57, 765, 1025, 2097, 4947, 9189, 103599, 216927, 4346128, 1558269, 1977777 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Subsequence of A109641. LINKS MATHEMATICA In[1]:= n = 1; Do[If[ !PrimeQ[k] && Mod[Binomial[3*k, k], k] == 3^n, Print[k]; n++ ], {k, 1, 10^4}] CROSSREFS Cf. A080469, A109641. Sequence in context: A277924 A095930 A026850 * A307570 A164589 A017950 Adjacent sequences:  A109639 A109640 A109641 * A109643 A109644 A109645 KEYWORD nonn AUTHOR Ryan Propper, Aug 05 2005 EXTENSIONS Edited by Max Alekseyev, Nov 03 2009 STATUS approved

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Last modified December 4 15:36 EST 2021. Contains 349526 sequences. (Running on oeis4.)