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 A124934 #14 Feb 11 2024 11:27:46 %S A124934 2,5,8,11,12,14,17,19,20,23,26,29,30,32,33,35,38,40,41,44,47,50,52,53, %T A124934 54,56,59,61,62,63,65,68,71,74,75,77,80,82,83,85,86,89,90,92,95,96,98, %U A124934 101,103,104,107,109,110,113,116,117,118,119,122,124,125,128,129,131 %N A124934 Numbers of the form 4mn - m - n, where m, n are positive integers. %C A124934 a(n) misses the squares since (2x)^2 + 1 = (4m - 1)(4n - 1) is impossible. %C A124934 a(n) misses the triangular numbers since (2x + 1)^2 + 1 = 2(4m - 1)(4n - 1) is impossible. %C A124934 Taking m = k(k - 1)/2, n = k(k + 1)/2 gives 4mn - m - n = (k^2 - 1)^2 - 1, so a(n) is one less than a square infinitely often. %C A124934 Complement of A094178; A125203(a(n)) > 0; union of A125217 and A125218; range of A125199. - _Reinhard Zumkeller_, Nov 24 2006 %D A124934 L. E. Dickson, History of the Theory of Numbers, Vol. II, Diophantine Analysis. Dover Publications, Inc., Mineola, NY, 2005, p. 401. %H A124934 N. Hobson, <a href="/A124934/b124934.txt">Table of n, a(n) for n = 1..1000</a> %e A124934 a(1) = 2 because 2 = 4*1*1 - 1 - 1 is the smallest value in the sequence. %o A124934 (Haskell) %o A124934 import Data.List (findIndices) %o A124934 a124934 n = a124934_list !! (n-1) %o A124934 a124934_list = map (+ 1) $ findIndices (> 0) a125203_list %o A124934 -- _Reinhard Zumkeller_, Jan 02 2013 %Y A124934 Cf. A000290, A000217. %K A124934 easy,nonn %O A124934 1,1 %A A124934 _Nick Hobson_, Nov 13 2006 %E A124934 More terms from _Reinhard Zumkeller_, Nov 24 2006