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A124272
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Primes in A124271[n], or primes of the form Sum[ (Prime[i]^n - 1) / (Prime[i] - 1), {i,1,n} ].
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4
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OFFSET
| 1,1
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COMMENTS
| A124271[n] = Sum[ (Prime[i]^n - 1) / (Prime[i] - 1), {i,1,n} ]. A124271[n] is prime for n = {2,8,14,...}.
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EXAMPLE
| A124271[n] begins {1,7,51,611,19839,603331,32981935,1469991559,...}.
Thus a(1) = 7 because A124271[2] = 7 is prime but A124271[1] = 1 is not prime.
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MATHEMATICA
| Do[f=Sum[(Prime[i]^n-1)/(Prime[i]-1), {i, 1, n}]; If[PrimeQ[f], Print[{n, f}]], {n, 1, 100}]
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CROSSREFS
| Cf. A124271, A124273, A124274, A124275, A123855, A123856.
Sequence in context: A116257 A075984 A109300 * A128820 A067485 A180225
Adjacent sequences: A124269 A124270 A124271 * A124273 A124274 A124275
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KEYWORD
| bref,hard,more,nonn
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AUTHOR
| Alexander Adamchuk (alex(AT)kolmogorov.com), Oct 23 2006
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