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URL: https://oeis.org/A118139

⇱ A118139 - OEIS

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A118139
Numbers expressible as the sum of two triangular numbers in at least two different ways.
5
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
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. A052343.
Sequence in context: A104392 A291746 A037001 * A087446 A340497 A051808
KEYWORD
easy,nonn
AUTHOR
Greg Huber, May 13 2006
EXTENSIONS
More terms from Reinhard Zumkeller, May 15 2006
STATUS
approved