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A118139 Numbers expressible as the sum of two triangular numbers in at least two different ways. 4
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 (list; graph; refs; listen; history; text; internal format)
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 A051808 A034053

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

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Last modified August 13 08:27 EDT 2020. Contains 336442 sequences. (Running on oeis4.)