A181742 - OEIS

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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).

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Table of n, a(n) for n=1..78.

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

Cf. A181741, A181743.

Sequence in context: A163400 A090972 A318241 * A179843 A319198 A243348

Adjacent sequences: A181739 A181740 A181741 * A181743 A181744 A181745

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Nov 08 2010

EXTENSIONS

Corrected and extended by Michel Marcus, Dec 17 2018

STATUS

approved