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 A094389 Last decimal digit of the odd Catalan number A038003(n). 4
 1, 1, 5, 9, 5, 9, 5, 9, 7, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Seems to be 5 for k >= 9. C_n is divisible by 5 whenever the base 5 expansion of n+1 contains a 4 or a non-final 3. The assertion that this sequence is 5 for n>=9 is thus equivalent to asserting that 2^n contains such a base 5 digit for n>=9. This is almost certainly true. - Franklin T. Adams-Watters, Feb 07 2006 Adams-Watters' surely-true statement verified for n < 50000. - David J. Rusin, Apr 21 2009 LINKS Eric Weisstein's World of Mathematics, Catalan Number MATHEMATICA (* first do *) Needs["DiscreteMath`CombinatorialFunctions`"] (* then *) Table[ Mod[ CatalanNumber[2^n - 1], 10], {n, 23}] (* Robert G. Wilson v *) (* or *) exp[fact_, num_] := Block[{k = 1, t = 0}, While[s = Floor[fact/num^k]; s > 0, t = t + s; k++ ]; t]; f[n_] := Block[{k = 2, m = 1}, While[p = Prime[k]; p <= n, m = Mod[m*p^(exp[2n, p] - 2exp[n, p]), 10]; k++ ]; While[p = Prime[k]; p < 2n, m = Mod[m*p, 10]; k++ ]; m]; Table[ f[2^n - 1], {n, 26}] (* Robert G. Wilson v, May 15 2004 *) CROSSREFS Cf. A000108, A038003. Sequence in context: A117014 A200283 A010720 * A057821 A133742 A134879 Adjacent sequences:  A094386 A094387 A094388 * A094390 A094391 A094392 KEYWORD nonn,base AUTHOR Eric W. Weisstein, Apr 28 2004 EXTENSIONS a(23) from Robert G. Wilson v, May 07 2004 a(24) & a(25) from Eric W. Weisstein, May 08 2004 a(26)-a(30) from Robert G. Wilson v, May 15 2004 More terms from David Wasserman, May 07 2007 STATUS approved

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Last modified May 7 00:22 EDT 2021. Contains 343609 sequences. (Running on oeis4.)