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A268607
a(n) is the least m > 1 such that 2^n - m is prime.
1
2, 3, 3, 3, 3, 15, 5, 3, 3, 9, 3, 13, 3, 19, 15, 9, 5, 19, 3, 9, 3, 15, 3, 39, 5, 39, 57, 3, 35, 19, 5, 9, 41, 31, 5, 25, 45, 7, 87, 21, 11, 57, 17, 55, 21, 115, 59, 81, 27, 129, 47, 111, 33, 55, 5, 13, 27, 55, 93, 31, 57, 25, 59, 49, 5, 19, 23, 19, 35
OFFSET
2,1
COMMENTS
a(1) is not defined (there are no primes less than 2).
The definition is similar to Lesser Fortunate numbers (A055211) but uses 2^n instead of primorials A002110(n).
EXAMPLE
a(7)=15 because m=15 is the least m > 1 such that 2^7 - m is prime.
PROG
(PARI) a(n)=2^n-precprime(2^n-2)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alexei Kourbatov, Feb 08 2016
STATUS
approved