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Search: id:A078746
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| A078746 |
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prime(2n(n+1)+1), where prime(n)=A000040(n) is the n-th prime. |
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+0
1
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| 2, 11, 41, 97, 179, 283, 439, 617, 829, 1087, 1381, 1697, 2081, 2467, 2909, 3433, 3929, 4517, 5119, 5801, 6481, 7237, 8059, 8863, 9739, 10663, 11701, 12659, 13729, 14867, 15973, 17239, 18443, 19843, 21179, 22549, 23971, 25541, 27043, 28657
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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Central elements of odd-length rows of the triangle of primes 2; 3,5; 7,11,13; ...
The sum of the reciprocals of the terms converges by comparison with sum_{n>=1} 1/n^2, since 1/a(n) < 1/(2n(n+1)+1) < 1/n^2. The limit is about 0.6471.
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PROGRAM
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(PARI) triprimes(n) = { sr = 0; for(j= 1, n, x = 2*j*(j-1) + 1; z = prime(x); sr+=1.0/z; print1(z" "); ); print(); print(sr); }
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CROSSREFS
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Cf. A078721.
Sequence in context: A000822 A154813 A080093 this_sequence A066593 A062256 A024522
Adjacent sequences: A078743 A078744 A078745 this_sequence A078747 A078748 A078749
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KEYWORD
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easy,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Dec 21 2002
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EXTENSIONS
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Edited by Dean Hickerson (dean.hickerson(AT)yahoo.com), Dec 23 2002
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