

A248983


Sequence of distinct least positive numbers such that the average of the first n terms is a triangular number.


1



1, 5, 3, 15, 6, 30, 10, 50, 69, 21, 98, 28, 132, 36, 171, 45, 215, 55, 264, 66, 318, 78, 377, 91, 441, 105, 510, 120, 584, 136, 663, 153, 747, 817, 190, 910, 210, 1008, 231, 1111, 253, 1219, 276, 1332, 300, 1450, 325, 1573, 351, 1701, 378, 1834, 406, 1972, 435, 2115, 465, 2263, 496
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OFFSET

1,2


LINKS

Table of n, a(n) for n=1..59.


EXAMPLE

1/1 = 1 is a triangular number. So a(1) = 1.
(1+2)/2 is not a triangular number. (1+3)/2 is not a triangular number. (1+4)/2 is not a triangular number. (1+5)/2 = 3 is a triangular number. So a(2) = 5.


PROG

(PARI) v=[]; n=1; while(n<5000, num=(vecsum(v)+n); if(num%(#v+1)==0&&vecsearch(vecsort(v), n)==0, for(i=1, n, if(i*(i+1)/2>(num/(#v+1)), break); if(i*(i+1)/2==(num/(#v+1)), print1(n, ", "); v=concat(v, n); n=1; break))); n++)


CROSSREFS

Cf. A000217.
Sequence in context: A213774 A167583 A329029 * A298975 A070375 A162813
Adjacent sequences: A248980 A248981 A248982 * A248984 A248985 A248986


KEYWORD

nonn


AUTHOR

Derek Orr, Oct 18 2014


STATUS

approved



