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 A008953 #34 Aug 04 2024 01:26:35 %S A008953 1,3,6,1,1,2,2,3,4,5,6,7,9,1,1,1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5, %T A008953 6,6,7,7,7,8,8,9,9,9,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2, %U A008953 2,2,2,2,2,2,2,2,3,3,3,3,3,3,3,3,3,3,3,3,4,4,4,4,4,4,4,4,4,4,4 %N A008953 a(n) is the leading digit of the n-th triangular number, n*(n+1)/2. %H A008953 Reinhard Zumkeller, <a href="/A008953/b008953.txt">Table of n, a(n) for n = 1..1000</a> %F A008953 a(n) = A000030(A000217(n)). - _Reinhard Zumkeller_, May 12 2010 %t A008953 Array[IntegerDigits[# (# + 1) / 2][[1]]&, 100] (* _Vincenzo Librandi_, Apr 12 2019 *) %t A008953 IntegerDigits[#][[1]]&/@Accumulate[Range[100]] (* _Harvey P. Dale_, Oct 15 2022 *) %o A008953 (PARI) a(n) = digits(n*(n+1)/2)[1]; \\ _Michel Marcus_, Jun 20 2018 %o A008953 (Magma) [Intseq((n*(n+1) div 2))[#Intseq((n*(n+1) div 2))]: n in [1..100]]; // _Vincenzo Librandi_, Apr 12 2019 %Y A008953 Cf. A000030, A000217, A008954. - _Reinhard Zumkeller_, May 12 2010 %K A008953 nonn,base,easy %O A008953 1,2 %A A008953 _N. J. A. Sloane_