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 A209685 #37 May 22 2025 10:21:35 %S A209685 0,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,10,2,3,4,5,6,7,8,9,10,11,3,4,5, %T A209685 6,7,8,9,10,11,12,4,5,6,7,8,9,10,11,12,13,5,6,7,8,9,10,11,12,13,14,6, %U A209685 7,8,9,10,11,12,13,14,15,7,8,9,10,11,12,13,14,15,16,8,9,10,11,12,13,14,15,16,17,9,10,11,12,13,14,15,16,17,18,0,1,2,3,4,5,6,7,8,9,1 %N A209685 Sum of last two digits of n. %C A209685 Note that "Sum of last three digits of n" takes the same values as this sequence for n <= 99 (but not for n = 100). "Sum of last three digits of n" repeats every 1000 terms, while this sequence repeats every 100 values. Analogs are obvious for "sum of the last 4 values of n" which repeats every 10^4 values. - _Jonathan Vos Post_, Mar 12 2012 [First sentence corrected by _N. J. A. Sloane_, Feb 12 2017] %H A209685 Indranil Ghosh, <a href="/A209685/b209685.txt">Table of n, a(n) for n = 0..1000</a> %H A209685 <a href="/index/Rec#order_100">Index entries for linear recurrences with constant coefficients</a>, signature (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1). %e A209685 99->9+9=18, 100->0+0=0. %o A209685 (PARI) a(n)=n%100\10+n%10 \\ _Charles R Greathouse IV_, Mar 11 2012 %o A209685 (Python) %o A209685 def A209685(n): %o A209685 if n<=9:return n %o A209685 return int(str(n)[-1])+int(str(n)[-2]) # _Indranil Ghosh_, Feb 12 2017 %Y A209685 Cf. A209674, A080463. Differs from A007953 and A076314 at n=100. %K A209685 nonn,base,easy %O A209685 0,3 %A A209685 _N. J. A. Sloane_, Mar 11 2012