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 A250202 #36 Aug 06 2017 10:20:49
%S A250202 6,36,9,81,117,162,38,13,2,4,16,17,26,8,64,41,34,104,128,164,66,61,26,
%T A250202 8,64,41,34,104,128,164,66,61,26,8,64,41,34,104,128,164,66,61,26,8,64,
%U A250202 41,34,104,128,164,66,61,26,8,64,41,34,104,128,164,66,61,26,8,64,41
%N A250202 The "sum of squares of digits" problem in base 12, start with 6 (written in base 10).
%C A250202 Periodic with period 10.
%C A250202 In base 12, there are 3 fixed points and 4 cycles (only 1 fixed point and 1 cycle in base 10, see A161772):
%C A250202 1 -> 1 (length 1);
%C A250202 5 -> 21 -> 5 (length 2);
%C A250202 8 -> 54 -> 35 -> 2a -> 88 -> a8 -> 118 -> 56 -> 51 -> 22 -> 8 (length 10);
%C A250202 18 -> 55 -> 42 -> 18 (length 3);
%C A250202 25 -> 25 (length 1);
%C A250202 68 -> 84 -> 68 (length 2);
%C A250202 a5 -> a5 (length 1);
%C A250202 Notice 25 (decimal 29) and a5 (decimal 125) are Armstrong numbers in base 12 (A161949), there are no 2-digit Armstrong numbers in base 10.
%C A250202 In base 12, there are only few happy numbers (no such between 10 (decimal 12) and 100 (decimal 144)), but in base 10, there are 20 happy numbers less than or equal to 100 (see A007770).
%H A250202 Eric Chen, <a href="/A250202/b250202.txt">Table of n, a(n) for n = 1..1000</a>
%H A250202 Eric Chen, <a href="/A250202/a250202.txt">List of A250202 starts with n for n up to 40 (decimal 48)</a>
%H A250202 <a href="/index/Rec#order_10">Index entries for linear recurrences with constant coefficients</a>, signature (0, 0, 0, 0, 0, 0, 0, 0, 0, 1).
%t A250202 NestList[Total[IntegerDigits[#, 12]^2]&, 6, 144]
%t A250202 Join[{6, 36, 9, 81, 117, 162, 38, 13, 2, 4, 16, 17},LinearRecurrence[{0, 0, 0, 0, 0, 0, 0, 0, 0, 1},{26, 8, 64, 41, 34, 104, 128, 164, 66, 61},54]] (* _Ray Chandler_, Aug 26 2015 *)
%t A250202 PadRight[{6,36,9,81,117,162,38,13,2,4,16,17},80,{66,61,26,8,64,41,34,104,128,164}] (* _Harvey P. Dale_, Aug 06 2017 *)
%o A250202 (PARI) a(n) = [6, 36, 9, 81, 117, 162, 38, 13, 2, 4, 16, 17, 26, 8, 64, 41, 34, 104, 128, 164, 66, 61][n%10+10*(n>=10)+10*(n%10<3 & n>=20)]
%Y A250202 Cf. A000216, A000218, A080709, A000221, A008460, A008461, A008462, A008463, A161772.
%K A250202 nonn,easy,base
%O A250202 1,1
%A A250202 _Eric Chen_, Mar 13 2015