A118139 Numbers expressible as the sum of two triangular numbers in at least two different ways.

6, 16, 21, 31, 36, 42, 46, 51, 55, 56, 66, 72, 76, 81, 91, 94, 106, 111, 120, 121, 123, 126, 133, 136, 141, 146, 156, 157, 171, 172, 174, 181, 186, 191, 196, 198, 210, 211, 216, 225, 226, 231, 237, 241, 246, 256, 259, 268, 276, 281, 286, 289, 291, 297, 301, 306

Offset

1,1

Comments

A052343(a(n)) > 1; gives A020756 together with A119345. - Reinhard Zumkeller, May 15 2006

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Example

a(1) = 6 = 0 + 6 = 3 +3.
a(2) = 16 = 1 + 15 = 6 + 10.
a(3) = 21 = 0 + 21 = 6 + 15.

Mathematica

Sort[Transpose[Select[Tally[Total/@(Union[Sort/@Tuples[Accumulate[ Range[ 0, 30]], 2]])], #[[2]]>1&]][[1]]] (* Harvey P. Dale, Jul 21 2015 *)

Prog

(Haskell)
a118139 n = a118139_list !! (n-1)
a118139_list = filter ((> 1) . a052343) [0..]
-- Reinhard Zumkeller, Jul 25 2014

Crossrefs

Cf. A020757, A000217.

Cf. A052343.

Sequence in context: A104392 A291746 A037001 * A087446 A340497 A051808

Adjacent sequences: A118136 A118137 A118138 * A118140 A118141 A118142

Keyword

easy,nonn

Author

Greg Huber, May 13 2006

Extensions

More terms from Reinhard Zumkeller, May 15 2006

Status

approved