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 A340520 #11 Jun 07 2025 18:39:07 %S A340520 1,3,5,9,13,17,23,29,35,41,49,57,65,73,81,91,101,111,121,131,141,153, %T A340520 165,177,189,201,213,225,239,253,267,281,295,309,323,337,353,369,385, %U A340520 401,417,433,449,465,481,499,517,535,553,571,589,607,625,643,661,681,701,721,741,761,781,801 %N A340520 a(n) = 2*A006463(n) + 1. %C A340520 Index of start of row n in b-files for triangles (such as A237593, A262045) where the rows have length 2*A003056(n). %H A340520 Hugo Pfoertner, <a href="/A340520/b340520.txt">Table of n, a(n) for n = 1..10000</a> %o A340520 (Python) %o A340520 from math import isqrt %o A340520 def A340520(n): return (m:=isqrt((n<<3)+1)-1>>1)*(6*n-2-m*(m+3))//3|1 # _Chai Wah Wu_, Jun 07 2025 %Y A340520 Cf. A003056, A006463, A237593, A262045. %K A340520 nonn %O A340520 1,2 %A A340520 _N. J. A. Sloane_, Feb 04 2021