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A123340
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Least m such that 2^n+3^m is prime.
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3
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0, 0, 0, 1, 0, 2, 1, 1, 0, 2, 2, 4, 1, 3, 3, 1, 0, 8, 1, 4, 8, 8, 6, 2, 7, 27, 6, 13, 1, 10, 1, 6, 4, 8, 18, 9, 19, 2, 15, 29, 3, 3, 17, 10, 3, 11, 6, 2, 5, 20, 34, 4, 12, 10, 26, 1, 4, 2, 9, 29, 29, 10, 34, 13, 4, 8, 2, 1, 8, 10, 26, 50, 19, 12, 10, 8, 13, 27, 17, 9, 33, 4, 2, 17, 1, 7, 3, 5, 61, 26
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OFFSET
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0,6
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LINKS
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EXAMPLE
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a(0)=0 because 2^0+3^0=1+1=2 is prime,
a(3)=1 because 2^3+3^1=8+3=11 is prime,
a(17)=8 because 2^17+3^8=131072+6561=137633 is prime,
a(25)=27 because 33554432+7625597484987=7625631039419 is prime, etc.
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MATHEMATICA
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a[n_] := Module[{m, t = 2^n}, For[m = 0, True, m++, If[PrimeQ[t + 3^m], Return[m]]]];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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