OFFSET
1,2
COMMENTS
This is the same as odd numbers not divisible by numbers of the form 2^(2^i) + 1, i >= 0.
Asymptotically, the number of such numbers <= x is x/4 + o(x).
Composite terms are 49, 77, 91, 121, 133, 143, 161, ... - Altug Alkan, Sep 14 2017
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
MATHEMATICA
Position[Table[DivisorSum[n, 1 &, IntegerQ@ Log2[# - 1] &], {n, 288}], 0][[All, 1]] (* Michael De Vlieger, Jun 11 2018 *)
PROG
(PARI) list(lim)=my(v=List(), u=[], t); lim\=1; forstep(n=1, lim, [4, 2], if(gcd(n, 1431655765)==1, listput(v, n))); v=Vec(v); for(i=5, logint(logint(lim-1, 2), 2), t=2^2^i+1; u=concat(u, t*[1..lim\t])); u=Set(u); setminus(v, u) \\ Charles R Greathouse IV, Sep 14 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Jeffrey Shallit, Sep 14 2017
STATUS
approved