OFFSET
1,2
COMMENTS
LINKS
FORMULA
a(n) = A138302(n)^2.
Sum_{n>=1} 1/a(n) = Product_{p prime} (1 + Sum_{k>=1} 1/p^(2^k)) = 1.62194750148969761827... .
MATHEMATICA
q[n_] := AllTrue[FactorInteger[n][[;; , 2]], # > 1 && # == 2^IntegerExponent[#, 2] &]; Select[Range[3300], # == 1 || q[#] &]
PROG
(PARI) is(n) = {my(e = factor(n)[, 2]); if(n == 1, 1, for(i = 1, #e, if(e[i] == 1 || e[i] >> valuation(e[i], 2) > 1, return(0))); 1); }
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Jan 26 2024
STATUS
approved