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A091554
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Primes p such that k = 2p is the smallest positive solution to the equation sigma(p+k) = sigma(p) + sigma(k).
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1
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7, 11, 13, 17, 19, 23, 31, 53, 59, 73, 79, 89, 97, 103, 109, 113, 137, 139, 149, 157, 163, 181, 193, 211, 223, 227, 269, 281, 293, 313, 331, 337, 373, 389, 397, 409, 419, 421, 433, 463, 467, 487, 499, 509, 521, 523, 541, 547, 571, 599, 601, 617, 631, 641, 643
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OFFSET
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1,1
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COMMENTS
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Note that for all primes p > 3, sigma(3p) = sigma(p) + sigma(2p).
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LINKS
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Table of n, a(n) for n=1..55.
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MATHEMATICA
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lst={}; Do[p=Prime[n]; k=1; While[DivisorSigma[1, p+k]!=DivisorSigma[1, p]+DivisorSigma[1, k], k++ ]; If[k==2p, AppendTo[lst, p]], {n, 3, 200}]; lst
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CROSSREFS
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Cf. A066435 (least k such that sigma(n+k)=sigma(n)+sigma(k)).
Sequence in context: A040121 A156114 A304690 * A111980 A108811 A038961
Adjacent sequences: A091551 A091552 A091553 * A091555 A091556 A091557
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KEYWORD
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nonn
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AUTHOR
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T. D. Noe, Jan 20 2004
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STATUS
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approved
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