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A111020 Indices of Catalan numbers (A000108) that are == 2 mod 3. 2
2, 3, 4, 8, 9, 10, 26, 27, 28, 38, 39, 40, 80, 81, 82, 92, 93, 94, 110, 111, 112, 116, 117, 118, 242, 243, 244, 254, 255, 256, 272, 273, 274, 278, 279, 280, 326, 327, 328, 332, 333, 334, 350, 351, 352, 362, 363, 364, 728, 729, 730, 740, 741, 742 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

MAPLE

filter:= proc(n) local L1, L2, L3;

  L1:= convert(2*n, base, 3);

  L2:= convert(n, base, 3);

  L3:= convert(n-1, base, 3);

  mul(binomial(L1[i], L2[i]), i=1..nops(L2)) - mul(binomial(L1[i], L3[i]), i=1..nops(L3)) mod 3 = 2

end proc:

select(filter, [$1..1000]); # Robert Israel, Jun 30 2020

MATHEMATICA

Flatten[Position[CatalanNumber[Range[750]], _?(Mod[#, 3]==2&)]] (* Harvey P. Dale, Sep 21 2012 *)

CROSSREFS

Cf. A000108.

Sequence in context: A079279 A246444 A045577 * A002971 A157318 A158031

Adjacent sequences:  A111017 A111018 A111019 * A111021 A111022 A111023

KEYWORD

nonn,look

AUTHOR

Robert G. Wilson v, Sep 09 2005

STATUS

approved

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Last modified April 17 19:51 EDT 2021. Contains 343070 sequences. (Running on oeis4.)