A118139 - OEIS

%I #10 Jul 21 2015 15:40:37

%S 6,16,21,31,36,42,46,51,55,56,66,72,76,81,91,94,106,111,120,121,123,

%T 126,133,136,141,146,156,157,171,172,174,181,186,191,196,198,210,211,

%U 216,225,226,231,237,241,246,256,259,268,276,281,286,289,291,297,301,306

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

%C A052343(a(n)) > 1; gives A020756 together with A119345. - _Reinhard Zumkeller_, May 15 2006

%H Reinhard Zumkeller, <a href="/A118139/b118139.txt">Table of n, a(n) for n = 1..10000</a>

%e a(1) = 6 = 0 + 6 = 3 +3.

%e a(2) = 16 = 1 + 15 = 6 + 10.

%e a(3) = 21 = 0 + 21 = 6 + 15.

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

%o (Haskell)

%o a118139 n = a118139_list !! (n-1)

%o a118139_list = filter ((> 1) . a052343) [0..]

%o -- _Reinhard Zumkeller_, Jul 25 2014

%Y Cf. A020757, A000217.

%Y Cf. A052343.

%K easy,nonn

%O 1,1

%A _Greg Huber_, May 13 2006

%E More terms from _Reinhard Zumkeller_, May 15 2006