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%I #30 Nov 13 2021 22:10:28
%S 16,36,81,100,196,225,441,484,625,676,1089,1156,1225,1444,1521,2116,
%T 2401,2601,3025,3249,3364,3844,4225,4761,5476,5929,6724,7225,7396,
%U 7569,8281,8649,8836,9025,11236,12321,13225,13924,14161,14641,14884,15129
%N Squares of semiprimes (A001358).
%C Disjoint union of 4th powers of primes, A030514, and squares of squarefree semiprimes, A085986. - _M. F. Hasler_, Nov 12 2021
%H Reinhard Zumkeller, <a href="/A074985/b074985.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) ~ (n log n/log log n)^2. - _Charles R Greathouse IV_, Oct 16 2015
%F Sum_{n>=1} 1/a(n) = (P(2)^2 + P(4))/2 = (A085548^2 + A085964)/2 = 0.1407604343..., where P is the prime zeta function. - _Amiram Eldar_, Oct 30 2020
%e 4 is divisible by 2 (twice) and 4*4 = 16.
%e 6 is divisible by exactly 2 and 3 and 6*6 = 36.
%p readlib(issqr): ts_kv_sp := proc(n); if (numtheory[bigomega](n)=4 and issqr(n)='true') then RETURN(n); fi; end: seq(ts_kv_sp(i), i=1..50000);
%t Select[Range[200],PrimeOmega[#]==2&]^2 (* _Harvey P. Dale_, Oct 03 2011 *)
%o (Haskell)
%o a074985 = a000290 . a001358 -- _Reinhard Zumkeller_, Aug 02 2012
%o (PARI) is(n)=if(issquare(n,&n), isprimepower(n)==2 || factor(n)[,2]==[1,1]~, 0) \\ _Charles R Greathouse IV_, Oct 16 2015
%o (PARI) list(lim)=lim=sqrtint(lim\1); my(v=List()); forprime(p=2, sqrtint(lim), forprime(q=p, lim\p, listput(v, (p*q)^2))); Set(v) \\ _Charles R Greathouse IV_, Nov 13 2021
%Y Cf. A001358, A085548, A085964.
%Y Cf. A030514 (4th powers of primes), A085986 (squares of squarefree semiprimes).
%K easy,nonn
%O 1,1
%A _Jani Melik_, Oct 07 2002
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