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Search: id:A166162
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| A166162 |
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Twin prime averages which are also the sum of the divisors of a triangular number. |
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+0
1
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| 4, 12, 18, 72, 192, 270, 1488, 1872, 1482, 1872, 1152, 2268, 6552, 3672, 6552, 10890, 3528, 5280, 7560, 7488, 13680, 23040, 17388, 29760, 21600, 23040, 65520, 87120, 51480, 34848, 65268, 127680, 122400, 134400, 114660, 137088, 206640, 134400
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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The triangular number A000217(3)= 6 has a sum of divisors 1+2+3+6 = 12 = A014574(3) which is also the average of the twin primes 11 and 13.
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MATHEMATICA
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t[n_]:=n*(n+1)/2; f[n_]:=Plus@@Divisors[t[n]]; lst={}; Do[p=f[n]; If[PrimeQ[p-1]&&PrimeQ[p+1], AppendTo[lst, p]], {n, 7!}]; lst
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CROSSREFS
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Cf. A074285, A014574 [R. J. Mathar, Oct 14 2008]
Sequence in context: A062859 A008237 A008120 this_sequence A086109 A139388 A008177
Adjacent sequences: A166159 A166160 A166161 this_sequence A166163 A166164 A166165
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KEYWORD
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nonn
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AUTHOR
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Vladimir Orlovsky (4vladimir(AT)gmail.com), Oct 08 2009
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EXTENSIONS
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Definition and example rewritten by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 14 2009
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