OFFSET
1,1
COMMENTS
Corresponding exponents of 2: 2, 3, 3, 39, 4, 4, 6, 5, 6, 5, 7, 11, 6, 29, 6, 6, 6, 6, 7, 10, 9, 9, 8, 8, 7, 1, 9, 8, 7, 10, 47, 14, 10, 9, 8, 31, 15, 9, 8, 8, 12, 9, 14, 21, 8, 9, 1, ...
LINKS
Robert Israel, Table of n, a(n) for n = 1..285
EXAMPLE
2 + 2 = 2^2,
3 + 5 = 2^3,
5 + 3 = 2^3,
7 + 549755813881 = 2^39,
11 + 5 = 2^4.
MAPLE
f:= proc(n) local p, m, t, q;
p:= ithprime(n);
for t from ilog2(p) do
q:= 2^t - p;
if isprime(q) then return q fi;
od;
end proc:
map(f, [$1..50]); # Robert Israel, Dec 23 2020
MATHEMATICA
f[p_] := NestWhile[2 # &, 2^Ceiling[Log[2, p]], ! PrimeQ[# - p] &] - p;
f /@ Prime@Range@47 (* David Trimas, Jul 30 2023 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov, Aug 28 2012
EXTENSIONS
a(26) corrected by Robert Israel, Dec 23 2020
STATUS
approved