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A113878 a(1)=0; a(n+1) is the least number > a(n) such that Sum_{k=1..n+1} 2^a(k) is not composite. 3
0, 1, 2, 4, 7, 16, 53, 66, 207, 1752, 5041, 6310 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Base-2 logarithms of A073924.

a(13) > 50000. - Don Reble

LINKS

Table of n, a(n) for n=1..12.

MATHEMATICA

a[1] = 0; a[n_] := a[n] = Block[{k = a[n - 1] + 1, s = Plus @@ (2^Array[a, n - 1])}, While[ !PrimeQ[s + 2^k], k++ ]; k]; Array[a, 12] (* Robert G. Wilson v *)

PROG

(Python)

from sympy import isprime

def afind(limit):

    print("0, 1", end=", ")

    s, pow2 = 2**0 + 2**1, 2**2

    for m in range(2, limit+1):

        if isprime(s+pow2): print(m, end=", "); s += pow2

        pow2 *= 2

afind(2000) # Michael S. Branicky, Jul 11 2021

CROSSREFS

Cf. A073924, A080355, A080567, A113824.

Sequence in context: A010355 A171880 A171874 * A293793 A301745 A348449

Adjacent sequences:  A113875 A113876 A113877 * A113879 A113880 A113881

KEYWORD

nonn,more

AUTHOR

Artur Jasinski, Jan 27 2006

EXTENSIONS

Edited by Don Reble, Feb 17 2006

STATUS

approved

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Last modified May 22 17:42 EDT 2022. Contains 353957 sequences. (Running on oeis4.)