This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A061208 #12 Jul 02 2025 16:02:01 %S A061208 1,3,4,6,7,9,10,11,13,14,15,16,17,18,19,20,21,22,24,25,26,27,28,29,30, %T A061208 31,32,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54, %U A061208 55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77 %N A061208 Numbers which can be expressed as sum of distinct triangular numbers (A000217). %C A061208 These numbers were called "almost-triangular" numbers during the Peru's Selection Test for the XII IberoAmerican Olympiad (1998). All numbers >= 34 are almost-triangular: see link. [_Bernard Schott_, Feb 04 2013] %H A061208 R. E. Woodrow, <a href="http://cms.math.ca/crux/v25/n4/page196-211.pdf">The Olympiad Corner, No. 198</a>, Crux Mathematicorum, v25-n4(2002), 207-208, exercise 2. %e A061208 25 = 1 + 3 + 6 + 15 %p A061208 gf := product(1+x^(j*(j+1)/2), j=1..100): s := series(gf, x, 200): for i from 1 to 200 do if coeff(s, x, i) > 0 then printf(`%d,`,i) fi:od: %Y A061208 Cf. A000217, A007294, A051611, A051533. Complement of A053614. %K A061208 nonn %O A061208 1,2 %A A061208 _Amarnath Murthy_, Apr 21 2001 %E A061208 Corrected and extended by _James Sellers_, Apr 24 2001