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A115908
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Numbers k such that phi(k) + prime(k) is a triangular number.
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3
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1, 5, 6, 15, 23, 141, 150, 258, 317, 340, 359, 378, 471, 503, 768, 1363, 2175, 2516, 3285, 3342, 3815, 3905, 4385, 4748, 5385, 5976, 6026, 6900, 7048, 7151, 7411, 7698, 8251, 8310, 8828, 10182, 10461, 12022, 12508, 13722, 13840, 15456, 16582
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OFFSET
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1,2
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LINKS
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EXAMPLE
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phi(503) + prime(503) = 4095 = T(90).
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MATHEMATICA
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With[{trnos = Accumulate[Range[5000]]}, Select[Range[20000], MemberQ[trnos, (EulerPhi[#] + Prime[#])] &]] (* Harvey P. Dale, Jan 12 2011 *)
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PROG
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(PARI) isok(n) = ispolygonal(prime(n) + eulerphi(n), 3); \\ Michel Marcus, Jan 25 2014
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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