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 A051266 #11 Aug 17 2017 22:38:39
%S A051266 7,11,13,15,16,17,19,21,22,23,25,26,27,28,29,32,33,34,35,36,38,39,40,
%T A051266 44,45,46,48,50,51,52,54,56,57,58,62,63,64,66,68,69,70,72,74,75,76,78,
%U A051266 80,82,84,86,88,90,92,94,96,98,100,102,104,105,108,110,112,114,120,126
%N A051266 Numbers n such that maximal value of prime divisors of reduced residue system for n is 2.
%C A051266 Largest value of A001221(k) = 2 for 1 <= k <= n such that gcd (k, n) = 1, i.e., k in row n of A038566. - _Michael De Vlieger_, Aug 10 2017
%H A051266 Michael De Vlieger, <a href="/A051266/b051266.txt">Table of n, a(n) for n = 1..161</a>
%e A051266 n = 29 is here because for terms of RRS(29) = {1, 2, ..., 27, 28} the number of prime divisors is 0(for 1), 1(for prime powers) or 2 (for 6, 10, 12, 14, 15, 18, 20, 21, 22, 24, 26, 28).
%t A051266 Block[{n = 2, P}, P = Product[Prime@ i, {i, n}]; P + Position[#, n][[All, 1]] &@ Array[Max@ Map[PrimeNu, Cases[Range@ #, k_ /; CoprimeQ[#, k]]] &, 120, P + 1]] (* _Michael De Vlieger_, Aug 10 2017 *)
%Y A051266 Cf. A001221, A002110, A038566, A048597, A051250, A051265, A051267, A051268.
%K A051266 nonn
%O A051266 1,1
%A A051266 _Labos Elemer_