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 A083534 #18 Feb 23 2025 02:40:54
%S A083534 2,2,2,2,2,1,1,2,2,2,2,2,1,1,2,2,2,1,1,2,1,1,2,2,2,2,2,1,1,2,2,2,2,2,
%T A083534 1,1,2,2,1,1,2,2,1,1,1,1,2,2,2,2,1,1,2,1,1,2,1,1,2,1,1,2,2,2,2,2,2,2,
%U A083534 1,1,2,1,1,2,1,1,1,1,2,2,2,2,1,1,2,2,2,1,1,2,1,1,2,2,1,1,1,1,2,1,1,2,2,2,2
%N A083534 First difference sequence of A007617. Difference between consecutive values not being in the range of phi (A000010).
%C A083534 a(n) is either 2 or 1 since odd numbers are in A007619.
%C A083534 If a(n) = 1 then A007619(n+1) is an even number not in the range of phi.
%H A083534 Reinhard Zumkeller, <a href="/A083534/b083534.txt">Table of n, a(n) for n = 1..10000</a>
%F A083534 a(n) = A007617(n+1) - A007617(n).
%e A083534 {11,13,14,15,17} are not in the range of phi and the corresponding differences are {2,1,1,2}.
%t A083534 t0[x_] := Table[j, {j, 1, x}]; t=Table[EulerPhi[w], {w, 1, 10000}]; u=Union[%]; c=Complement[t0[10000], u]; Delete[c-RotateRight[c], 1]
%o A083534 (Haskell)
%o A083534 a083534 n = a083534_list !! (n-1)
%o A083534 a083534_list = zipWith (-) (tail a007617_list) a007617_list
%o A083534 -- _Reinhard Zumkeller_, Nov 26 2015
%o A083534 (PARI) list(lim) = {my(k1 = 3, k2 = 3); while(k1 < lim, until(!istotient(k2), k2++); print1(k2 - k1, ", "); k1 = k2); } \\ _Amiram Eldar_, Feb 22 2025
%Y A083534 Cf. A000010, A002202, A005277, A007617, A007619, A083531, A083532, A083533, A083535, A083536.
%K A083534 nonn
%O A083534 1,1
%A A083534 _Labos Elemer_, May 20 2003