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A115908 Numbers n such that phi(n) plus the n-th prime is a triangular number. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..43.

EXAMPLE

phi(503)+prime(503)=4095=T(90).

MATHEMATICA

With[{trnos = Accumulate[Range[5000]]}, Select[Range[20000], MemberQ[trnos, (EulerPhi[#] + Prime[#])] &]] (* Harvey P. Dale, Jan 12 2011 *)

PROG

(PARI) isok(n) = ispolygonal(prime(n) + eulerphi(n), 3); \\ Michel Marcus, Jan 25 2014

CROSSREFS

Cf. A115882, A115907.

Sequence in context: A121847 A030533 A227066 * A247962 A241307 A185876

Adjacent sequences:  A115905 A115906 A115907 * A115909 A115910 A115911

KEYWORD

nonn

AUTHOR

Giovanni Resta, Feb 06 2006

STATUS

approved

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Last modified October 14 17:31 EDT 2019. Contains 328022 sequences. (Running on oeis4.)