

A130317


Smallest number having exactly n triangular divisors.


10



1, 3, 6, 36, 30, 90, 180, 210, 420, 630, 1890, 1260, 2520, 6930, 18480, 20790, 13860, 27720, 41580, 83160, 138600, 245700, 235620, 180180, 556920, 360360, 540540, 1670760, 1081080, 1413720, 2702700, 2162160, 6486480, 3063060, 8288280
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,2


COMMENTS

2*a(n) is smallest number having exactly n oblong divisors.
A007862(a(n)) = n and A007862(m) <> n for m < a(n).


LINKS

Ray Chandler and Donovan Johnson, Table of n, a(n) for n = 1..100 (first 58 terms from Ray Chandler)


FORMULA

a(n) = A088726(n1)/2 for n>1.  Ray Chandler, Jun 24 2008


EXAMPLE

a(3)=6: A007862(6)=#{1,2*(2+1)/2,3*(3+1)/2}=3;
a(4)=36: A007862(36)=#{1,2*(2+1)/2,3*(3+1)/2,8*(8+1)/2}=4;


PROG

(PARI) a(n) = my(k=1); while (sumdiv(k, d, ispolygonal(d, 3)) != n, k++); k; \\ Michel Marcus, Jan 14 2022


CROSSREFS

Cf. A007862, A088726, A130279.
Sequence in context: A009197 A205336 A184390 * A019467 A106128 A119186
Adjacent sequences: A130314 A130315 A130316 * A130318 A130319 A130320


KEYWORD

nonn


AUTHOR

Reinhard Zumkeller, May 23 2007


EXTENSIONS

Extended by Ray Chandler, Jun 24 2008


STATUS

approved



