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 A019469 Numbers n such that n does not divide binomial(2*n-4, n-2). 4
 2, 3, 4, 6, 8, 9, 12, 15, 16, 27, 30, 32, 33, 36, 39, 42, 64, 81, 84, 87, 90, 93, 96, 108, 111, 114, 117, 120, 123, 128, 243, 246, 249, 252, 255, 256, 258, 270, 273, 276, 279, 282, 285, 324, 327, 330, 333, 336, 339 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Previous name was: Numbers n such that (n-2)-nd Catalan number is not divisible by n. Conjecture: sequence is union of powers of two > 1 (A000079) and 3 * A096304. LINKS Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 MAPLE A019469:=n->`if`(binomial(2*n-4, n-2) mod n <> 0, n, NULL): seq(A019469(n), n=1..400); # Wesley Ivan Hurt, Sep 13 2014 MATHEMATICA Select[Range[400], !Divisible[Binomial[2#-4, #-2], #]&] (* Harvey P. Dale, Aug 13 2015 *) PROG (PARI) valp(n, p)=my(s); while(n\=p, s+=n); s bin(n, p)=valp(2*n, p)-2*valp(n, p) is(n)=my(f=factor(n)); for(i=1, #f~, if(bin(n-2, f[i, 1])

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Last modified October 15 22:25 EDT 2019. Contains 328038 sequences. (Running on oeis4.)