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 A074985 Squares of semiprimes (A001358). 10
 16, 36, 81, 100, 196, 225, 441, 484, 625, 676, 1089, 1156, 1225, 1444, 1521, 2116, 2401, 2601, 3025, 3249, 3364, 3844, 4225, 4761, 5476, 5929, 6724, 7225, 7396, 7569, 8281, 8649, 8836, 9025, 11236, 12321, 13225, 13924, 14161, 14641, 14884, 15129 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Disjoint union of 4th powers of primes, A030514, and squares of squarefree semiprimes, A085986. - M. F. Hasler, Nov 12 2021 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 FORMULA a(n) ~ (n log n/log log n)^2. - Charles R Greathouse IV, Oct 16 2015 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 EXAMPLE 4 is divisible by 2 (twice) and 4*4 = 16. 6 is divisible by exactly 2 and 3 and 6*6 = 36. MAPLE 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); MATHEMATICA Select[Range[200], PrimeOmega[#]==2&]^2 (* Harvey P. Dale, Oct 03 2011 *) PROG (Haskell) a074985 = a000290 . a001358 -- Reinhard Zumkeller, Aug 02 2012 (PARI) is(n)=if(issquare(n, &n), isprimepower(n)==2 || factor(n)[, 2]==[1, 1]~, 0) \\ Charles R Greathouse IV, Oct 16 2015 (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 CROSSREFS Cf. A001358, A085548, A085964. Cf. A030514 (4th powers of primes), A085986 (squares of squarefree semiprimes). Sequence in context: A125240 A050775 A022040 * A229134 A069262 A076956 Adjacent sequences: A074982 A074983 A074984 * A074986 A074987 A074988 KEYWORD easy,nonn AUTHOR Jani Melik, Oct 07 2002 STATUS approved

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Last modified August 9 21:53 EDT 2024. Contains 375044 sequences. (Running on oeis4.)