OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
Sum_{n>=1} 1/a(n) = P(2)^2/2 + P(4)/2 - P(2)/4 = 0.02769857933..., where P is the prime zeta function. - Amiram Eldar, Mar 22 2021
EXAMPLE
9 is odd and divisible by 3 (twice) and 9*9=81.
15 is odd and divisible by 3 and 5 and 15*15=225.
MAPLE
readlib(issqr): ts_kv_sp_lih := proc(n); if (numtheory[bigomega](n)=4 and type(n, odd)='true' and issqr(n)='true') then RETURN(n); fi; end: seq(ts_kv_sp_lih(i), i=1..100000);
MATHEMATICA
Select[Range[1, 201, 2], PrimeOmega[#] == 2 &]^2 (* Amiram Eldar, Mar 22 2021 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jani Melik, Oct 07 2002
EXTENSIONS
Checked by Zak Seidov, Mar 08 2006
STATUS
approved