

A218392


Primitive triangle numbers as defined in A218243.


2



60, 150, 200, 780, 1530, 1690, 1950, 2040, 2100, 2730, 2860, 3570, 4056, 4200, 4350, 4624, 5100, 5460, 8120, 8250, 8670, 8750, 10812, 11050, 11900, 12180, 13260, 13650, 14060, 14430, 14760, 15540, 17220, 17850, 18564, 19240, 23400, 24420, 26100, 26520, 27880, 29172, 30000
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,1


COMMENTS

Triangle numbers A218243 are integers n = a*b*c such that the triangle with sides (a,b,c) has integer area. For any such n, n*k^3 is again an element of A218243 for any integer k>0. Terms in A218243 which are not of that form (with k>1) are called "primitive", and listed here.


LINKS



EXAMPLE

The term A218243(4)=480 is not in this sequence since 480 = 2^3*60 and 60 = A218243(1).
The number n=30000=A218243(67) is divisible by 10^3, but neither of n/2^3, n/5^3, n/10^3 is in A218243, therefore n is in this sequence.


PROG

(PARI) is_A218392(n)=is_A218243(n)  return; my(f=factor(n)); vecmax(f[, 2])<3  !fordiv(factorback(Mat(apply(t>[t[1], t[2]\3]~, Vec(f~)))~), d, d>1 & is_A218243(n/d^3) & return)


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



