A123360 Least m such that 5^n+2^m is prime.

0, 1, 2, 1, 4, 7, 2, 5, 12, 5, 2, 15, 8, 5, 10, 37, 24, 1, 14, 17, 28, 41, 16, 145, 44, 101, 8, 35, 64, 43, 74, 63, 24, 35, 16, 13, 88, 81, 14, 53, 44, 21, 46, 89, 56, 7, 70, 97, 200, 59, 8, 35, 24, 45, 22, 53, 12, 77, 6, 19, 4, 165, 18, 5, 488, 157, 26, 101, 120, 59, 4, 115, 44, 89

Offset: 0

Author

Zak Seidov, Oct 12 2006

Keywords

• nonn

Examples

			a(0)=0 because 5^0+2^0=1+1=2 is prime,
a(5)=7 because 5^5+2^7=3125+128=3253 is prime,
		

Crossrefs

Cf. A123340 = least m such that 2^n+3^m is prime, A123342 = least m such that 2^n+5^m is prime.

Cf. A123340, A123342.

Programs

Mathematica

lm[n_]:=Module[{c=5^n,m=1},While[CompositeQ[c+2^m],m++];m]; Join[ {0},Array[lm,80]] (* Harvey P. Dale, Jul 18 2021 *)