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A088183
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Number of ways to write n as a sum of two coprime semiprimes.
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4
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0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 2, 0, 0, 0, 1, 0, 1, 0, 0, 0, 2, 0, 3, 0, 0, 1, 1, 0, 2, 0, 2, 0, 2, 0, 4, 1, 0, 1, 4, 0, 2, 0, 1, 0, 3, 0, 4, 0, 1, 2, 5, 0, 6, 0, 1, 3, 1, 0, 4, 1, 3, 0, 6, 0, 5, 3, 1, 2, 3, 0, 5, 0, 3, 2, 7, 0, 1, 3, 4, 1, 4, 0, 6, 2, 2, 3, 6, 0, 7, 1, 4, 2, 6, 1
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OFFSET
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1,19
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COMMENTS
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Is a(n)>0 for n>210? see conjecture in A072931.
The graph of this sequence is compelling evidence that 210 is the last term of sequence A088185. - T. D. Noe, Apr 10 2007
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LINKS
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Eric Weisstein's World of Mathematics, Semiprime
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EXAMPLE
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a(64)=3: 64 = 3*3+5*11 = 3*5+7*7 = 5*5+3*13, (A072931(64)=5).
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MATHEMATICA
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cpspQ[{a_, b_}]:=PrimeOmega[a]==PrimeOmega[b]==2&&CoprimeQ[a, b]; Table[ Count[ IntegerPartitions[n, {2}], _?(cpspQ[#]&)], {n, 110}] (* Harvey P. Dale, Sep 10 2019 *)
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PROG
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(PARI) a(n)=sum(i=1, n, sum(j=1, i, if (gcd(i, j)==1, if (abs(bigomega(i)-2) +abs(bigomega(j)-2) +abs(n-i-j), 0, 1)))) \\ after A072966; Michel Marcus, Sep 08 2015
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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