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).

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

Author

Vladimir Shevelev, Nov 08 2010

Keywords

• nonn

Crossrefs

Cf. A181741, A181743.

Programs

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 *)

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

Extensions

Corrected and extended by Michel Marcus, Dec 17 2018