A051611 Numbers that are not the sum of 2 nonzero triangular numbers.

1, 3, 5, 8, 10, 14, 15, 17, 19, 23, 26, 28, 32, 33, 35, 40, 41, 44, 45, 47, 50, 52, 53, 54, 59, 62, 63, 68, 71, 74, 75, 77, 78, 80, 82, 85, 86, 89, 95, 96, 98, 103, 104, 105, 107, 109, 113, 116, 117, 118, 122, 124, 125, 128, 129, 131, 134, 138, 140, 143, 145, 147

Offset

1,2

Comments

A053603(a(n)) = 0. - Reinhard Zumkeller, Jun 28 2013

Links

T. D. Noe, Table of n, a(n) for n=1..1000

Mathematica

notSumQ[n_] := Reduce[ 0 < x <= y && n == x*(x + 1)/2 + y*(y + 1)/2, {x, y}, Integers] === False; Select[ Range[150], notSumQ] (* Jean-François Alcover, Jun 27 2012 *)
With[{trnos=Accumulate[Range[100]]}, Complement[Range[150], Total/@ Tuples[ trnos, 2]]] (* Harvey P. Dale, Jun 01 2016 *)

Prog

(Haskell)
a051611 n = a051611_list !! (n-1)
a051611_list = filter ((== 0) . a053603) [1..]
-- Reinhard Zumkeller, Jun 28 2013

Crossrefs

Integers not in the sequence A051533. Cf. A002097, A000217, A007294, A051611, A053603.

Sequence in context: A091309 A027922 A097911 * A258028 A345427 A005004

Adjacent sequences: A051608 A051609 A051610 * A051612 A051613 A051614

Keyword

easy,nonn,nice

Author

Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de)

Status

approved