A159268 Largest m<=n such that 2^m+3^n is prime, 0 if no such m exists.

0, 1, 2, 2, 4, 3, 5, 6, 7, 4, 9, 6, 7, 7, 10, 14, 11, 8, 14, 0, 9, 20, 19, 18, 23, 12, 19, 25, 25, 11, 26, 28, 25, 10, 15, 6, 35, 30, 27, 34, 31, 24, 19, 37, 36, 34, 38, 32, 23, 48, 41, 50, 44, 47, 0, 28, 41, 52, 54, 48, 52, 52, 39, 53, 56, 63, 17, 57, 63, 14, 62, 60, 55, 54, 59, 17, 56

Offset

0,3

Comments

For n>0, a(n)=0 means that there is no such m, since 2^0+3^n cannot be prime for n>0.

Links

Table of n, a(n) for n=0..76.

Example

a(0)=0 since 2^0+3^0=2 is prime.
a(18)=14 is the largest integer m <= 18 such that 2^m+3^18 is prime.
a(19)=0 since there is no integer m <= 19 such that 2^m+3^19 is prime.

Prog

(PARI) A159268(n)=forstep(m=n, 1, -1, is/*pseudo*/prime(2^m+3^n) & return(m))

Crossrefs

Sequence in context: A329437 A318632 A094051 * A058723 A329436 A182577

Adjacent sequences: A159265 A159266 A159267 * A159269 A159270 A159271

Keyword

nonn

Author

M. F. Hasler, Apr 07 2009

Status

approved