OFFSET
1,14
COMMENTS
0's occur only at Mersenne prime exponents (A000043) - 1, twos are in A092112, threes do not appear < 504.
a(n) <= 2 for n <= 2000. - Robert Israel, Mar 05 2020
LINKS
Robert Israel, Table of n, a(n) for n = 1..2000
FORMULA
a(n) = n+1 - A091937(n).
MAPLE
f:= proc(n) local t, j, k;
t:= 2^(n+1)-1;
if isprime(t) then return 0 fi;
for j from 1 to n-1 do if isprime(t-2^j) then return 1 fi od;
for j from 1 to n-2 do for k from j+1 to n-1 do
if isprime(t-2^j-2^k) then return 2 fi od od;
FAIL
end proc:
map(f, [$1..200]); # Robert Israel, Mar 05 2020
MATHEMATICA
Compute the second line of the Mathematica code for A091938, then (Table[n + 1, {n, 105}]) - (Count[ IntegerDigits[ #, 2], 1] & /@ Table[ f[n], {n, 105}])
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Feb 20 2004
STATUS
approved