OFFSET
1,1
COMMENTS
Numbers of this form can be represented in the numeral system described in A235860 with k - 1 ones followed to the right by k - 1 twos or k ones followed to the right by k - 1 twos, like this: 1, 12, 112, 1122, 11122, 111222, 1111222, ... (1, 3, 4, 8, 9, 17, 18, ... in decimal) and are the least numbers that need one more digit to be represented than any of their predecessors.
The corresponding sequence of primes starts 3, 17, 67, 1031, 1180591620717411303491, ...
MATHEMATICA
fQ[n_] := PrimeQ[2^n + n - If[ OddQ@ n, 2, 3]]; Select[ Range@ 30000, fQ]
PROG
(PARI) isok(n) = isprime(2^n + n - 3) || isprime(2^n + n - 2); \\ Michel Marcus, Feb 13 2014
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robin Garcia, Feb 13 2014
EXTENSIONS
a(21)-a(22) from Robert G. Wilson v, Mar 03 2014
a(23) from Michael S. Branicky, May 01 2023
a(24) from Michael S. Branicky, Jul 30 2024
STATUS
approved