

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(n1)) / 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(n1)^2) / n is an integer. T(i) = ith 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



