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 A169821 #7 Mar 30 2012 17:38:11 %S A169821 0,1,4,0,7,7,0,4,1,0,100,121,144,160,187,117,130,154,171,100,400,441, %T A169821 484,430,477,427,460,414,451,400,0,61,34,0,67,37,0,64,31,0,700,781, %U A169821 774,760,757,747,730,724,711,700,700,711,724,730,747,757,760,774,781,700,0,31,64 %N A169821 a(n) = n*n in carryless arithmetic mod 9 in base 10. %C A169821 Addition and multiplication are the same as in school, that is, done in base 10, except that there are no carries and individual digits are added or multiplied mod 9. %H A169821 <a href="/index/Ca#CARRYLESS">Index entries for sequences related to carryless arithmetic</a> %e A169821 13*13 = 160: %e A169821 ..13 %e A169821 ..13 %e A169821 ---- %e A169821 ..30 %e A169821 .13. %e A169821 ---- %e A169821 .160 %e A169821 ---- %Y A169821 Cf. A010878, A169908. See A170990 for a better version. %K A169821 nonn,base %O A169821 0,3 %A A169821 _David Applegate_, _Marc LeBrun_ and _N. J. A. Sloane_, Jul 11 2010