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A123674 a(n) = number of primes of the form 2^n - 3^k. 0
0, 1, 2, 2, 4, 2, 3, 2, 4, 2, 2, 2, 3, 3, 1, 2, 4, 0, 3, 4, 4, 3, 3, 3, 0, 1, 1, 0, 2, 1, 1, 1, 3, 2, 3, 2, 2, 0, 1, 2, 2, 3, 0, 0, 4, 4, 3, 2, 5, 4, 4, 0, 0, 0, 1, 1, 4, 5, 2, 4, 3, 3, 0, 1, 1, 2, 5, 0, 1, 1, 4, 3, 1, 0, 1, 1, 3, 2, 3, 0, 2, 4, 2, 1, 2, 2, 3, 0, 7, 2, 4, 4, 2, 2, 2, 3, 5, 0, 3, 1, 1, 1, 3, 3, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

a(1) = 0 because there are no prime numbers of the form 2^1 - 3^k. a(2) = 1 because the only prime of the form 2^2 - 3^k is 2^2 - 3^0 = 3. a(3) = because there are two primes of the form 2^3 - 3^k: 2^3 - 3^0 = 7 and 2^3 - 3^1 = 5.

LINKS

Table of n, a(n) for n=1..105.

MATHEMATICA

Table[Length[Select[Range[0, Floor[Log[3, 2^n]]], PrimeQ[2^n-3^# ]&]], {n, 1, 200}]

CROSSREFS

Sequence in context: A127796 A131287 A102640 * A092607 A221861 A057939

Adjacent sequences:  A123671 A123672 A123673 * A123675 A123676 A123677

KEYWORD

nonn

AUTHOR

Alexander Adamchuk, Nov 17 2006

STATUS

approved

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Last modified May 18 04:35 EDT 2013. Contains 225419 sequences.