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A113878
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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.
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3
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0, 1, 2, 4, 7, 16, 53, 66, 207, 1752, 5041, 6310
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internal format)
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OFFSET
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1,3
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COMMENTS
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Base-2 logarithms of A073924.
a(13) > 50000. - Don Reble
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LINKS
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Table of n, a(n) for n=1..12.
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MATHEMATICA
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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 *)
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PROG
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(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
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CROSSREFS
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Cf. A073924, A080355, A080567, A113824.
Sequence in context: A010355 A171880 A171874 * A293793 A301745 A348449
Adjacent sequences: A113875 A113876 A113877 * A113879 A113880 A113881
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KEYWORD
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nonn,more
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AUTHOR
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Artur Jasinski, Jan 27 2006
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EXTENSIONS
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Edited by Don Reble, Feb 17 2006
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STATUS
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approved
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