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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
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
Sequence in context: A010355 A171880 A171874 * A293793 A301745 A348449
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 March 18 22:50 EDT 2024. Contains 370951 sequences. (Running on oeis4.)