OFFSET
1,2
COMMENTS
Numbers in whose prime factorization the exponent of 2 can be only 0 or 1, and the exponent of any odd prime can be only 0 or 2.
FORMULA
Sum_{n>=1} 1/a(n) = 18/Pi^2. - Amiram Eldar, Jan 07 2023
MATHEMATICA
Select[Range[6000], (e = IntegerExponent[#, 2]) < 2 && SquareFreeQ[Sqrt[#/2^e]] &] (* Amiram Eldar, Jan 07 2023 *)
PROG
(PARI) isA359580(n) = A359549(n);
(Python)
from itertools import count, islice
from sympy import factorint
def A359580_gen(startvalue=1): # generator of terms >= startvalue
return filter(lambda n:(m:=(~n & n-1).bit_length())<=1 and all(e==2 for e in factorint(n>>m).values()), count(max(startvalue, 1)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Jan 07 2023
STATUS
approved