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Search: id:A066885
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| A066885 |
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(p(n)^2+1)/2, where p(n) is the n-th prime. |
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+0
10
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| 5, 13, 25, 61, 85, 145, 181, 265, 421, 481, 685, 841, 925, 1105, 1405, 1741, 1861, 2245, 2521, 2665, 3121, 3445, 3961, 4705, 5101, 5305, 5725, 5941, 6385, 8065, 8581, 9385, 9661, 11101, 11401, 12325, 13285, 13945, 14965, 16021, 16381, 18241, 18625
(list; graph; listen)
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OFFSET
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2,1
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COMMENT
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a(n) is the average of the numbers from 1 to p(n)^2. It's also the average of the primes in a p(n) by p(n) example of Haga's conjecture (see link below).
If a(n) is a square c^2, then p(n) is a NSW prime (A088165) and a prime RMS number (A140480). [From Ctibor O. Zizka (ctibor.zizka(AT)seznam.cz), Aug 26 2008]
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LINKS
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Carlos Rivera, The prime puzzles & problems connection, conjecture 26
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MATHEMATICA
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a[n_] := (Prime[n]^2+1)/2
lst={}; Do[AppendTo[lst, (DivisorSigma[2, Prime[n]])/2], {n, 2, 5!}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Mar 11 2009]
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CROSSREFS
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Cf. A066883, A066886.
Sequence in context: A146140 A146283 A026373 this_sequence A147151 A057288 A107466
Adjacent sequences: A066882 A066883 A066884 this_sequence A066886 A066887 A066888
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KEYWORD
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easy,nonn
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AUTHOR
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Enoch Haga (Enokh(AT)comcast.net), Jan 22 2002
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EXTENSIONS
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Edited by Dean Hickerson (dean.hickerson(AT)yahoo.com), Jun 08 2002
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