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A295769 Triangular numbers that can be represented as a product of two triangular numbers greater than 1, and as a product of three triangular numbers greater than 1. 3
630, 990, 4095, 15400, 19110, 25200, 37128, 61425, 79800, 105570, 122265, 145530, 176715, 192510, 437580, 500500, 749700, 828828, 1185030, 2031120, 2162160, 2821500, 4279275, 4573800, 4744740, 4959675, 5364450, 6053460, 7556328, 8817900, 13857480, 15992340 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Duplicates in the products are allowed.

A subsequence of A188630.

LINKS

Table of n, a(n) for n=1..32.

EXAMPLE

630 = 105*6 = 21*10*3.

990 = 66*15 = 55*6*3.

MAPLE

A295769 := proc(limit) local t, E, G, n, k, j, c, b, d, ist; E:=NULL; G:=NULL;

t := proc(n) option remember; iquo(n*(n+1), 2) end;

ist := proc(n) option remember; n = t(floor(sqrt(2*n))) end;

for n from 2 do

    c := t(n); if c > limit then break fi;

    for k from 2 do

        b := c*t(k); if b > limit then break fi;

        if ist(b) then E := E, b fi;

        for j from 2 do

            d := b*t(j); if d > limit then break fi;

            if ist(d) then G := G, d fi

od od od; {E} intersect {G} end:

A295769(200000); # Peter Luschny, Dec 21 2017

CROSSREFS

Cf. A000217, A188630.

Sequence in context: A177421 A333503 A173423 * A110904 A171258 A234245

Adjacent sequences:  A295766 A295767 A295768 * A295770 A295771 A295772

KEYWORD

nonn

AUTHOR

Alex Ratushnyak, Nov 27 2017

STATUS

approved

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Last modified June 1 04:37 EDT 2020. Contains 334758 sequences. (Running on oeis4.)