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 A261694 #29 Sep 08 2022 08:46:13
%S A261694 0,1,1,2,3,5,8,13,0,13,13,5,18,2,20,1,0,1,1,2,3,5,8,13,0,13,13,5,18,2,
%T A261694 20,1,0,1,1,2,3,5,8,13,0,13,13,5,18,2,20,1,0,1,1,2,3,5,8,13,0,13,13,5,
%U A261694 18,2,20,1,0,1,1,2,3,5,8,13,0,13,13,5,18,2,20,1,0,1,1,2,3,5,8,13,0,13
%N A261694 a(n) = Fibonacci(n) mod 21.
%C A261694 Sequence is periodic with Pisano period 16; Pisano number 21 in the sequence A001175. The only other sequence with Pisano period 16 is that of A105870 which is the Fibonacci sequence mod 7. This is Pisano number 7.
%H A261694 G. C. Greubel, <a href="/A261694/b261694.txt">Table of n, a(n) for n = 0..1000</a> [a(391) = 13 corrected by _Georg Fischer_, May 24 2019]
%F A261694 G.f.: x*(1 + x + 2*x^2 + 3*x^3 + 5*x^4 + 8*x^5 + 13*x^6 + 13*x^8 + 13*x^9 + 5*x^10 + 18*x^11 + 2*x^12 + 20*x^13 + x^14)/(1-x^16).
%t A261694 Table[Mod[Fibonacci[n], 21], {n, 0, 100}]
%t A261694 PadRight[{},120,{0,1,1,2,3,5,8,13,0,13,13,5,18,2,20,1}] (* _Harvey P. Dale_, May 16 2020 *)
%o A261694 (Magma) [Fibonacci(n) mod 21: n in [0..120]]; // _Vincenzo Librandi_, Nov 19 2015
%o A261694 (PARI) a(n) = fibonacci(n)%21; \\ _Altug Alkan_, Nov 19 2015
%o A261694 (Python)
%o A261694 A261694_list, a, b, = [], 0, 1
%o A261694 for _ in range(10**3):
%o A261694 A261694_list.append(a)
%o A261694 a, b = b, (a+b) % 21 # _Chai Wah Wu_, Nov 26 2015
%Y A261694 Cf. A000045, A001175, A105870,
%K A261694 nonn,easy
%O A261694 0,4
%A A261694 _G. C. Greubel_, Nov 18 2015