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 A066561 #25 Apr 22 2025 02:38:06
%S A066561 1,6,3,28,10,6,21,120,36,10,55,36,78,28,15,496,136,36,171,120,21,66,
%T A066561 253,120,300,78,351,28,406,120,465,2016,66,136,105,36,666,190,78,120,
%U A066561 820,210,903,528,45,276,1081,528,1176,300,153,780,1378,378,55,1176,171
%N A066561 a(n) is the smallest triangular number divisible by n.
%C A066561 See A344005 for an efficient algorithm. - _N. J. A. Sloane_, Jul 13 2021
%H A066561 T. D. Noe, <a href="/A066561/b066561.txt">Table of n, a(n) for n = 1..1000</a>
%F A066561 a(n) = A000217(A011772(n)). - _Bill McEachen_, Dec 28 2021
%F A066561 a(n) = A344005(2*n)*(A344005(2*n)+1)/2. - _Chai Wah Wu_, Apr 21 2025
%o A066561 (PARI) { for (n=1, 1000, s=0; b=0; while (b==0, s++; t=s*(s+1)/2; if (t%n == 0, b=1)); write("b066561.txt", n, " ", t) ) } \\ _Harry J. Smith_, Mar 05 2010
%Y A066561 Cf. A000217, A011772, A344005, A345988.
%K A066561 nonn
%O A066561 1,2
%A A066561 _Amarnath Murthy_, Dec 17 2001
%E A066561 More terms from _Naohiro Nomoto_, Dec 26 2001