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A166602 Numbers k such that Sum_{i=1..k} i^2 divides Product_{i=1..k} i^2. 7
1, 7, 13, 17, 19, 24, 25, 27, 31, 32, 34, 37, 38, 43, 45, 47, 49, 55, 57, 59, 61, 62, 64, 67, 71, 73, 76, 77, 79, 80, 84, 85, 87, 91, 92, 93, 94, 97, 101, 103, 104, 107, 109, 110, 115, 117, 118, 121, 122, 123, 124, 127, 129, 132, 133, 137, 139, 142, 143, 144, 145, 147 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Product_{i=1..k} i^2 = (k!)^2 and Sum_{i=1..k} i^2 = k(k-1)(2k-1)/6. - _J. Mulder_ (jasper.mulder(AT)planet.nl), Jan 25 2010

LINKS

J. Mulder, Table of n, a(n) for a(n) below 20000

EXAMPLE

a(2) = A125314(2) = 7.

MATHEMATICA

Cases[Range[2, 5000], k_ /; Divisible[Factorial[k - 1]^2, 1/6 (-1 + k) k (-1 + 2 k)]] - 1 (* _J. Mulder_ (jasper.mulder(AT)planet.nl), Jan 25 2010 *)

CROSSREFS

Cf. A125314, A060462, A166604, A166605, A166606, A166607, A166608, A166609, A166610.

Cf. A067656. [From R. J. Mathar, Oct 23 2009]

Sequence in context: A233518 A118942 A067656 * A079697 A079695 A079698

Adjacent sequences:  A166599 A166600 A166601 * A166603 A166604 A166605

KEYWORD

nonn

AUTHOR

Alexander Adamchuk, Oct 18 2009

EXTENSIONS

Terms below 5000 by J. Mulder (jasper.mulder(AT)planet.nl), Jan 25 2010

More terms copied from the b-file by R. J. Mathar, Feb 14 2010

STATUS

approved

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Last modified April 24 12:21 EDT 2019. Contains 322429 sequences. (Running on oeis4.)