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A209309 Numbers whose sum of triangular divisors is also triangular and greater than 1. 3
6, 12, 18, 24, 48, 54, 96, 102, 110, 114, 138, 162, 174, 186, 192, 204, 220, 222, 228, 246, 258, 282, 315, 318, 348, 354, 364, 366, 372, 384, 402, 414, 426, 438, 440, 444, 456, 474, 486, 492, 498, 516, 522, 534, 550, 558, 564, 582, 606, 618, 636, 642, 654, 678 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Antonio Roldán, Table of n, a(n) for n = 1..8055 (a(n) <= 10^5)

EXAMPLE

186 is in sequence because the sum of its triangular divisors, 1+3+6 = 10 is also triangular

PROG

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

{t=0; for(n=1, 10^5, k=sumdiv(n, d, istriangular(d)*d); if(istriangular(k)&&k>>1, t+=1; write("b209309.txt", t, " ", n)))}

CROSSREFS

Cf. A185027, A035316.

Sequence in context: A031478 A073455 A279894 * A020333 A044831 A033003

Adjacent sequences:  A209306 A209307 A209308 * A209310 A209311 A209312

KEYWORD

nonn

AUTHOR

Antonio Roldán, Jan 18 2013

STATUS

approved

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Last modified December 15 11:43 EST 2019. Contains 329999 sequences. (Running on oeis4.)