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A115911 Numbers n such that phi(n) times sigma(n) is a triangular number. 0
1, 2, 9, 11, 23, 118, 373, 556, 1332, 2420, 3081, 5251, 7642, 12671, 116836, 127627, 135861, 172676, 198912, 365408, 421902, 426710, 901273, 921736, 954068, 1001396, 1003333, 1006567, 1077452, 1161754, 1162514, 1364225, 1632361 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..33.

EXAMPLE

phi(1003333)*sigma(1003333)=1003888529280=T(1416960).

PROG

(PARI) isok(n) = ispolygonal(eulerphi(n)*sigma(n), 3); \\ Michel Marcus, Jan 09 2014

CROSSREFS

Cf. A062354, A069066.

Sequence in context: A041581 A042463 A081613 * A065596 A280418 A042053

Adjacent sequences:  A115908 A115909 A115910 * A115912 A115913 A115914

KEYWORD

nonn

AUTHOR

Giovanni Resta, Feb 06 2006

STATUS

approved

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Last modified April 22 10:22 EDT 2019. Contains 322330 sequences. (Running on oeis4.)