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 A073078 Least k such that n divides C(2k,k). 2
 1, 1, 2, 3, 3, 2, 4, 7, 5, 3, 6, 5, 7, 4, 8, 15, 9, 5, 10, 3, 5, 6, 12, 7, 13, 7, 14, 5, 15, 8, 16, 31, 6, 9, 4, 5, 19, 10, 7, 13, 21, 5, 22, 6, 8, 12, 24, 15, 25, 13, 11, 7, 27, 14, 8, 11, 11, 15, 30, 14, 31, 16, 5, 63, 8, 6, 34, 9, 14, 4, 36, 14, 37, 19, 14, 10, 6, 7, 40, 15, 41, 21 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 FORMULA a(2^k)=2^k-1, if n is an odd prime a(n)=(n+1)/2 (but there are also some composites satisfying this property, see A079290). MAPLE A073078 := proc(n)     for k from 1 do         if modp(binomial(2*k, k), n) = 0 then             return k;         end if;     end do: end proc: # R. J. Mathar, Aug 20 2014 MATHEMATICA lk[n_]:=Module[{k=1}, While[!Divisible[Binomial[2k, k], n], k++]; k]; Array[lk, 90] (* Harvey P. Dale, Oct 09 2012 *) PROG (PARI) a(n)=if(n<0, 0, s=1; while(binomial(2*s, s)%n>0, s++); s) CROSSREFS Sequence in context: A131469 A309076 A343326 * A034799 A008985 A326699 Adjacent sequences:  A073075 A073076 A073077 * A073079 A073080 A073081 KEYWORD easy,nonn AUTHOR Benoit Cloitre, Aug 17 2002 STATUS approved

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Last modified August 17 17:59 EDT 2022. Contains 356189 sequences. (Running on oeis4.)