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A140973 Numbers n such that arithmetic mean of squares of the first n tribonacci numbers is an integer. 1
1, 2, 8, 15, 16, 18, 22, 32, 47, 48, 53, 58, 64, 70, 77, 78, 80, 94, 95, 96, 103, 106, 128, 138, 163, 199, 206, 256, 257, 266, 269, 311, 326, 330, 352, 358, 385, 397, 398, 401, 419, 421, 499, 512, 514, 538, 587, 599, 617, 622, 640, 672, 683, 757, 768, 770, 773 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Could arithmetic tribonacci mean (T(0)+...+T(n-1)) / n be an integer?

The arithmetic means are integers for the first 1, 2, 47, 53, 94, 103, 106 etc. tribonacci numbers. - R. J. Mathar, Aug 04 2008

LINKS

Table of n, a(n) for n=1..57.

FORMULA

n such that (T(0)^2+ T(1)^2+ ... + T(n-1)^2) / n is an integer. T(i) = i-th tribonacci number.

CROSSREFS

Cf. A000073.

Cf. A107239. - R. J. Mathar, Aug 04 2008

Sequence in context: A054981 A059449 A272930 * A065907 A031272 A277139

Adjacent sequences:  A140970 A140971 A140972 * A140974 A140975 A140976

KEYWORD

easy,nonn

AUTHOR

Ctibor O. Zizka, Jul 27 2008

EXTENSIONS

Added 1 and 2 and extended from 32 on, R. J. Mathar, Aug 04 2008

STATUS

approved

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Last modified October 27 05:51 EDT 2020. Contains 338035 sequences. (Running on oeis4.)