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 A181743 The exponent k which defines A181741(n) = 2^t-2^k-1. 1
 2, 1, 3, 2, 1, 3, 1, 5, 4, 2, 1, 7, 6, 5, 4, 2, 7, 5, 3, 1, 5, 2, 1, 3, 9, 7, 4, 2, 1, 11, 13, 10, 8, 6, 1, 11, 7, 4, 11, 3, 17, 14, 13, 9, 8, 6, 5, 4, 2, 11, 19, 18, 17, 14, 12, 11, 10, 9, 7, 4, 2, 1, 17, 9, 7, 3, 16, 10, 5, 4, 1, 21, 15, 13, 10, 5, 4, 1, 13, 9, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS FORMULA k = A007814(A181741(n)+1). [R. J. Mathar, Nov 18 2010] MATHEMATICA IntegerExponent[Select[Table[2^t-2^k-1, {t, 1, 20}, {k, 1, t-1}] // Flatten // Union, PrimeQ] + 1, 2] (* Amiram Eldar, Dec 17 2018 after Jean-François Alcover at A181741 *) PROG (PARI) listk(nn) = {for (n=3, nn, forstep(k=n-1, 1, -1, if (isprime(2^n-2^k-1), print1(k, ", ")); ); ); } \\ Michel Marcus, Dec 17 2018 CROSSREFS Cf. A181741, A181742. Sequence in context: A240554 A107338 A118123 * A330727 A174737 A131756 Adjacent sequences:  A181740 A181741 A181742 * A181744 A181745 A181746 KEYWORD nonn AUTHOR Vladimir Shevelev, Nov 08 2010 EXTENSIONS Terms equivalent to insertions in A181741 inserted by R. J. Mathar, Nov 18 2010 More terms from Michel Marcus, Dec 17 2018 STATUS approved

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Last modified June 18 01:16 EDT 2021. Contains 345098 sequences. (Running on oeis4.)