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Search: id:A156780
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| 0, 0, 2, 10, 10, 30, 30, 68, 68, 68, 68, 140, 140, 246, 246, 246, 246, 406, 406, 616, 616, 616, 616, 900, 900, 900, 900, 900, 900, 1290, 1290, 1760, 1760, 1760, 1760, 1760, 1760, 2364, 2364, 2364, 2364, 3094, 3094, 3934, 3934, 3934, 3934, 4920, 4920, 4920
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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All terms are even, since the parity of sp(n)=A034387(n) is always the opposite of pi(n)=A000720(n). Indeed, both change by an odd amount at each prime, starting with the first nonzero values sp(2)=2 and pi(2)=1. Thus one might also consider the integer sequence a(n)/2 = 0, 0, 1, 5, 5, 15, 15, 34, 34, 34, 34, 70, 70, 123, 123, 123, 123, 203, 203, 308,.... Sequence A156778 lists these values (without duplicates).
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FORMULA
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a(n) = 2*A156778( pi(n)), where pi(n) = A000720(n)= PrimePi(n) = #{primes <= n}.
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PROGRAM
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(PARI) vector(80, n, sum(i=1, primepi(n), prime(i))*primepi(n))
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CROSSREFS
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Sequence in context: A066556 A156556 A071808 this_sequence A067046 A066394 A033466
Adjacent sequences: A156777 A156778 A156779 this_sequence A156781 A156782 A156783
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KEYWORD
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nonn
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AUTHOR
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M. F. Hasler (MHasler(AT)univ-ag.fr), Feb 21 2009
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