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A181742
Let A181741(n)=2^(t(n))-2^(k(n))-1, where k(n)>=1, t(n)>=k(n)+1. Then a(n)=t(n).
1
3, 3, 4, 4, 4, 5, 5, 6, 6, 6, 6, 8, 8, 8, 8, 8, 9, 9, 9, 9, 10, 10, 10, 11, 12, 12, 12, 12, 12, 13, 14, 14, 14, 14, 14, 16, 16, 16, 17, 17, 18, 18, 18, 18, 18, 18, 18, 18, 18, 19, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 21, 21, 21, 21, 22, 22, 22, 22, 22, 24, 24, 24, 24, 24, 24, 24
OFFSET
1,1
MATHEMATICA
f[n_] := IntegerExponent[n + 2^IntegerExponent[n, 2], 2]; f/@ (Select[Table[2^t-2^k-1, {t, 1, 20}, {k, 1, t-1}] // Flatten // Union, PrimeQ] + 1) (* Amiram Eldar, Dec 17 2018 after Jean-François Alcover at A181741 *)
PROG
(PARI) listt(nn) = {for (n=3, nn, forstep(k=n-1, 1, -1, if (isprime(2^n-2^k-1), print1(n, ", ")); ); ); } \\ Michel Marcus, Dec 17 2018
CROSSREFS
Sequence in context: A163400 A090972 A318241 * A179843 A319198 A243348
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Nov 08 2010
EXTENSIONS
Corrected and extended by Michel Marcus, Dec 17 2018
STATUS
approved