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 A261306 #4 Aug 22 2015 05:20:45
%S A261306 1,0,17,16,15,10,9,8,7,6,5,4,3,2,1,0,101,100,99,98,97,96,95,94,93,62,
%T A261306 61,60,59,58,57,56,55,54,53,52,39,38,37,36,35,34,33,32,31,30,29,28,27,
%U A261306 26,25,24,23,22,21,20,19,18,17,16,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1,0,461,460,459,458,457,456
%N A261306 a(n+1) = abs((n) - gcd(a(n), 6*n+5)), a(1) = 1.
%C A261306 It is conjectured that for all n, a(n) = 0 implies that a(n+1) = 6n+5 is prime, cf. A186258. (This is the sequence {u(n)} mentioned there.)
%e A261306 a(2) = a(1) - gcd(a(1),6+5) = 1 - 1 = 0.
%e A261306 a(3) = |a(2) - gcd(a(2),6*2+5)| = gcd(0,17) = 17 is prime.
%e A261306 a(5) = 15, thus a(6) = 15 - gcd(15,6*5+5) = 15 - 5 = 10; similarly after a(25) = 93.
%o A261306 (PARI) print1(a=1);for(n=1,199,print1(",",a=abs(a-gcd(a,6*n+5))))
%Y A261306 Cf. A261301 - A261310, A186253 - A186263, A106108.
%K A261306 nonn
%O A261306 1,3
%A A261306 _M. F. Hasler_, Aug 14 2015