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 A282355 Expansion of (Sum_{i>=1} x^prime(prime(i)))*(Sum_{j = p*q, p prime, q prime} x^j). 2
 0, 0, 0, 0, 0, 0, 0, 1, 0, 2, 0, 1, 1, 1, 1, 2, 0, 2, 1, 1, 2, 2, 0, 1, 1, 2, 3, 2, 1, 1, 1, 2, 2, 1, 0, 1, 2, 3, 3, 2, 2, 2, 2, 2, 2, 3, 2, 1, 0, 2, 3, 3, 3, 1, 2, 2, 4, 2, 1, 0, 3, 1, 3, 4, 1, 3, 4, 2, 4, 3, 2, 1, 2, 3, 4, 2, 3, 3, 0, 3, 5, 2, 4, 0, 1, 3, 2, 3, 4, 4, 3, 2, 5, 5, 3, 0, 5, 4, 6, 3, 3, 1, 3, 2, 3, 5, 3, 0, 4, 2, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,10 COMMENTS Number of ways of writing n as a sum of a prime with prime subscript (A006450) and a semiprime (A001358). Every sufficiently large even number can be written as the sum of two primes, or a prime and a semiprime (Chen's theorem). Conjecture: a(n) > 0 for all n > 527 (addition: only 18 positive integers cannot be represented as a sum of a prime number with prime subscript and a semiprime). LINKS Ilya Gutkovskiy, Extended graphical example FORMULA G.f.: (Sum_{i>=1} x^prime(prime(i)))*(Sum_{j = p*q, p prime, q prime} x^j). EXAMPLE a(9) = 2 because we have [6, 3] and [5, 4]. MATHEMATICA nmax = 110; CoefficientList[Series[Sum[x^Prime[Prime[k]], {k, 1, nmax}] Sum[Floor[PrimeOmega[k]/2] Floor[2/PrimeOmega[k]] x^k, {k, 2, nmax}], {x, 0, nmax}], x] CROSSREFS Cf. A001358, A006450, A100949. Sequence in context: A306440 A025905 A115861 * A199322 A284203 A341594 Adjacent sequences:  A282352 A282353 A282354 * A282356 A282357 A282358 KEYWORD nonn AUTHOR Ilya Gutkovskiy, Feb 13 2017 STATUS approved

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Last modified December 3 04:53 EST 2021. Contains 349445 sequences. (Running on oeis4.)