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 A120623 Numbers n such that the n-th Catalan number C(2n, n)/(n + 1) is divisible by n/3 but not divisible by n. 4
 3, 12, 18, 84, 99, 120, 198, 216, 273, 342, 432, 522, 540, 792, 828, 945, 975, 984, 990, 1035, 1071, 1323, 1377, 1512, 1548, 1575, 1710, 1755, 1863, 2052, 2106, 2226, 2385, 2442, 2790, 2928, 3009, 3015, 3132, 3198, 3483, 3672, 3807, 3915, 3996, 4212, 4428 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Chai Wah Wu, Table of n, a(n) for n = 1..10000 MATHEMATICA fQ[n_] := fQ[n_] := IntegerQ[ Binomial[2n, n]/(n(n + 1)/3)] && !IntegerQ[ Binomial[2n, n]/n]; Select[ Range@4463, fQ@# &] PROG (Python) A120623_list, b = [], 1 for n in range(1, 10**5): if b % n and not (3*b) % n: A120623_list.append(n) b = b*(4*n+2)//(n+2) # Chai Wah Wu, Mar 30 2016 CROSSREFS Cf. A000108, A014847, A120622. Sequence in context: A342785 A166038 A052637 * A158517 A043877 A217697 Adjacent sequences: A120620 A120621 A120622 * A120624 A120625 A120626 KEYWORD nonn AUTHOR Robert G. Wilson v, Jun 19 2006 EXTENSIONS Better description from Joel B. Lewis, Nov 15 2006 STATUS approved

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Last modified April 19 08:45 EDT 2024. Contains 371782 sequences. (Running on oeis4.)