

A107757


Numbers k such that Sum_{j=1..k} Catalan(j) == 2 (mod 3).


3



3, 9, 11, 27, 29, 35, 39, 81, 83, 89, 93, 107, 111, 117, 119, 243, 245, 251, 255, 269, 273, 279, 281, 323, 327, 333, 335, 351, 353, 359, 363, 729, 731, 737, 741, 755, 759, 765, 767, 809, 813, 819, 821, 837, 839, 845, 849, 971, 975, 981, 983, 999, 1001, 1007, 1011
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OFFSET

1,1


LINKS

Table of n, a(n) for n=1..55.
Y. More, Problem 11165, Amer. Math. Monthly, 112 (2005), 568.


MAPLE

c:=n>binomial(2*n, n)/(n+1): s:=0: for n from 1 to 1500 do s:=s+c(n): a[n]:=s mod 3: od: A:=[seq(a[n], n=1..1500)]: p:=proc(n) if A[n]=2 then n else fi end: seq(p(n), n=1..1500); # Emeric Deutsch, Jun 12 2005


MATHEMATICA

s0 = s2 = {}; s = 0; Do[s = Mod[s + (2 n)!/n!/(n + 1)!, 3]; Switch[ Mod[s, 3], 0, AppendTo[s0, n], 2, AppendTo[s2, n]], {n, 1055}]; s2 (* Robert G. Wilson v, Jun 14 2005 *)


CROSSREFS

Cf. A000108, A107755, A107756.
Equals A074939  1.
Sequence in context: A032915 A019080 A060141 * A191180 A191128 A057261
Adjacent sequences: A107754 A107755 A107756 * A107758 A107759 A107760


KEYWORD

nonn,easy


AUTHOR

N. J. A. Sloane, Jun 11 2005


EXTENSIONS

More terms from Emeric Deutsch, Jun 12 2005


STATUS

approved



