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 A072931 Number of ways to write n as a sum of 2 semiprimes. 9
 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 2, 2, 2, 1, 0, 1, 2, 2, 1, 1, 2, 2, 3, 3, 2, 0, 1, 3, 3, 2, 1, 3, 3, 2, 3, 4, 4, 2, 1, 4, 5, 3, 3, 1, 3, 3, 2, 5, 3, 2, 2, 5, 6, 6, 1, 3, 5, 3, 4, 4, 5, 3, 3, 6, 7, 5, 3, 3, 4, 4, 4, 5, 5, 3, 2, 7, 7, 2, 4, 4, 5, 4, 6, 8, 6, 3, 3, 8, 7, 7, 4, 6, 8, 6, 5, 7, 7, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,18 COMMENTS Sequence is probably > 0 for n > 33. The graph of this sequence is compelling evidence that 33 is the last term of sequence A072966. - T. D. Noe, Apr 10 2007 LINKS T. D. Noe, Table of n, a(n) for n=1..10000 FORMULA From Reinhard Zumkeller, Jan 21 2010: (Start) a(A100592(n)) = n; a(m) < n for m < A100592(n); A171963(n) = a(A001358(n)). (End) a(n) = Sum_{i=1..floor(n/2)} [Omega(i) == 2] * [Omega(n-i) == 2], where Omega = A001222 and [] is the Iverson Bracket. - Wesley Ivan Hurt, Apr 04 2018 MATHEMATICA lim = 10000; s = Select[Range[lim], PrimeOmega[#] == 2 &]; c = Tally[ Sort[ Map[ Total, Union[Subsets[s, {2}],       Table[{s[[i]], s[[i]]}, {i, 1, Length[s]}]]]]]; a = Table[0, lim]; i=1; While[c[[i]] [[1]]<=lim, a[[c[[i]] [[1]]]]=c[[i]] [[2]]; i++]; a (* Robert Price, Mar 30 2019 *) PROG (PARI) a(n)=sum(i=1, n, sum(j=1, i, if(abs(bigomega(i)-2) + abs(bigomega(j)-2) + abs(n-i-j), 0, 1))) (PARI) a(n)=my(s); forprime(p=2, n\4, forprime(q=2, min(n\(2*p), p), if(bigomega(n-p*q)==2, s++))); s \\ Charles R Greathouse IV, Dec 07 2014 CROSSREFS Cf. A001222, A001358, A072966, A101048. Sequence in context: A334888 A039981 A006140 * A307013 A307012 A112211 Adjacent sequences:  A072928 A072929 A072930 * A072932 A072933 A072934 KEYWORD easy,nonn AUTHOR Benoit Cloitre, Aug 13 2002 STATUS approved

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Last modified September 27 00:14 EDT 2020. Contains 337378 sequences. (Running on oeis4.)