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A124271
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Sum[ (Prime[i]^n - 1) / (Prime[i] - 1), {i,1,n} ].
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4
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1, 7, 51, 611, 19839, 603331, 32981935, 1469991559, 108336139407, 17389027481287, 1334783150250945, 222909199163881075, 31099653342061054699, 2994181661163361882651, 387134597481460117602345
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| a(n) is prime for n = {2,8,14,...}. Prime a(n) are listed in A124272[n] = {7,1469991559,2994181661163361882651,...}. Primes p that divide a(p) are listed in A124273[n] = {3,7,13,17,19,31,47,59,61,71,101,103,107,109,137,149,151,157,167,197,...}, that almost coincides with A123856[n]. Up to 1000 there are only 3 terms of A123856[n] that are different from the terms of a(n). They are listed in A124275[n] = {2,5,181}. Nonprime n that divide a(n) are listed in A124274[n] = {1,9,15,121,...}.
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FORMULA
| a(n) = Sum[ (Prime[i]^n - 1) / (Prime[i] - 1), {i,1,n} ].
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MATHEMATICA
| Table[Sum[(Prime[i]^n-1)/(Prime[i]-1), {i, 1, n}], {n, 1, 20}]
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CROSSREFS
| Cf. A124272, A124273, A124274, A124275, A123855, A123856.
Sequence in context: A019472 A081216 A198087 * A198007 A156751 A138849
Adjacent sequences: A124268 A124269 A124270 * A124272 A124273 A124274
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KEYWORD
| nonn
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AUTHOR
| Alexander Adamchuk (alex(AT)kolmogorov.com), Oct 23 2006
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