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 A250209 a(n) = least k such that k * n is in A072226, or 0 if no such k exists. 1
 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 5, 1, 2, 2, 1, 2, 1, 6, 1, 1, 2, 5, 1, 1, 1, 1, 1, 8, 34, 8, 1, 2, 1, 10, 1, 2, 350, 2, 1, 111, 4, 1, 3, 16, 4, 15, 28, 3, 1, 206, 3, 10, 2, 1, 1, 2, 3, 1, 15, 637, 12, 1, 4, 22, 17, 104, 4, 2, 1012, 1, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Conjecture: a(n) > 0 for all n. Numbers n such that n * a(n) > 10^5, a(n) is currently unknown for n = 121, 124, 130, 143, 144, 162, 164, 171, 172, 185, 188, 197, 201, 215, ... a(121) = (A117545(2048))/11 and they are both currently unknown. A117545(2^n) = a(A064549(n)). LINKS Eric Chen, Table of n, a(n) for n = 1..120 Eric Chen, Table of n, a(n) for n = 1..300 status MATHEMATICA Table[k=1; while[!PrimeQ[Cyclotomic[n*k, 2]], k++]; k, {n, 150}] PROG (PARI) a(n) = {k = 1; while (!isprime(polcyclo(k*n, 2)), k++); k; } \\ Michel Marcus, Jan 18 2015 CROSSREFS Sequence in context: A160094 A043283 A127937 * A280010 A167852 A184340 Adjacent sequences:  A250206 A250207 A250208 * A250210 A250211 A250212 KEYWORD nonn AUTHOR Eric Chen, Jan 18 2015 STATUS approved

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Last modified October 18 14:52 EDT 2019. Contains 328161 sequences. (Running on oeis4.)