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A209310 Triangular numbers whose sum of triangular divisors is also triangular and greater than 1. 2
6, 4186, 32131, 52975, 78210, 111628, 237016, 247456, 584821, 750925, 1464616, 3649051, 5791906, 11297881, 16082956, 24650731, 27243271, 38618866, 46585378, 51546781, 56026405, 76923406, 89880528, 96070591, 126906346, 164629585, 201854278, 228733966 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..1000

EXAMPLE

4186 is in sequence because it is triangular (4186 = 91*92/2) and the sum of triangular divisors, 4186+91+1 = 4278 is also triangular (4278 = 92*93/2)

PROG

(PARI) istriangular(n)=issquare(8*n+1)

{t=0; for(n=1, 10^8, if(istriangular(n), k=sumdiv(n, d, istriangular(d)*d) ; if(istriangular(k)&&k>>1, t+=1; write("b209310.txt", t, " ", n))))}

CROSSREFS

Cf. A185027, A035316, A209309.

Sequence in context: A024087 A161845 A317485 * A268504 A099723 A226499

Adjacent sequences:  A209307 A209308 A209309 * A209311 A209312 A209313

KEYWORD

nonn

AUTHOR

Antonio Roldán, Jan 18 2013

STATUS

approved

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Last modified December 7 00:16 EST 2019. Contains 329812 sequences. (Running on oeis4.)