OFFSET
1,1
COMMENTS
FORMULA
a(n) = 2*A000037(n).
EXAMPLE
The divisors of 14 are {1, 2, 7, 14}, two of them: 2 and 14 are even, hence 14 is a term.
The divisors of 16 are {1, 2, 4, 8, 16}, four of them: 2, 4, 8 and 16 are even, hence 16 is another term.
MAPLE
filter:= q -> irem(q, 2) = 0 and sqrt(q/2) <> floor(sqrt(q/2)) : select(filter, [$1..156]);
MATHEMATICA
m = 9; 2 * Complement[Range[m^2], Range[m]^2] (* Amiram Eldar, Oct 02 2021 *)
PROG
(PARI) isok(k) = !(k % 2) && !(sumdiv(k, d, !(d % 2)) % 2); \\ Michel Marcus, Oct 05 2021
(Python)
from math import isqrt
def A348005(n): return n+(m:=isqrt(n))+int(n-m*(m+1)>=1)<<1 # Chai Wah Wu, Aug 04 2022
CROSSREFS
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| Integers with | an even number of ... | an odd number of ... |
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KEYWORD
nonn
AUTHOR
Bernard Schott, Oct 02 2021
STATUS
approved