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A064828 Numbers which are the sum of two positive triangular numbers in exactly three different ways. 1
81, 106, 156, 181, 211, 256, 276, 331, 361, 381, 406, 456, 556, 606, 631, 666, 681, 706, 718, 731, 781, 856, 861, 931, 939, 956, 981, 1051, 1131, 1206, 1231, 1406, 1456, 1506, 1563, 1606, 1631, 1681, 1731, 1732, 1756, 1831, 1891, 1901, 1956, 1981, 2081 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harry J. Smith, Table of n, a(n) for n = 1..500

EXAMPLE

81 = 45 + 36 = 66 + 15 = 78 + 3.

MATHEMATICA

Take[Transpose[Select[Split[Sort[Total/@(Union[Sort/@Tuples[Accumulate[ Range[300]], {2}]])]], Length[#]==3&]][[1]], 60] (* Harvey P. Dale, Jun 04 2011 *)

PROG

(PARI) Tri(n)= { n*(n + 1)/2 } { n=0; for (m=1, 10^9, k=0; i=1; until (t>=m\2 || k>3, t=Tri(i); j=i; i++; until (s>=m || k>3, s=t + Tri(j); j++; if (s==m, k++))); if (k==3, write("b064828.txt", n++, " ", m); if (n==1000, return)) ) } [Harry J. Smith, Sep 27 2009]

CROSSREFS

Cf. A000217, A064816.

Sequence in context: A256349 A202002 A249613 * A265135 A265136 A120457

Adjacent sequences: A064825 A064826 A064827 * A064829 A064830 A064831

KEYWORD

nonn

AUTHOR

Jonathan Ayres (jonathan.ayres(AT)btinternet.com), Oct 23 2001

STATUS

approved

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Last modified December 1 08:58 EST 2022. Contains 358467 sequences. (Running on oeis4.)