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 A141229 #12 Sep 12 2019 15:03:02 %S A141229 27,43,109,125,157,229,277,283,307,499,643,691,733,739,811,997,1021, %T A141229 1051,1069,1093,1331,1459,1579,1597,1627,1699,1723,1789,1933,2179, %U A141229 2197,2203,2251,2341,2347,2749,2917,3163,3181,3229,3259,3373,4027,4339,4549,4597,4651,4909 %N A141229 Odd numbers k for which A006694((k-1)/2) = 3. %C A141229 Conjecture. The terms of the sequence have only one prime divisor; moreover, p^3 is in the sequence if and only if p is in A001122. %H A141229 Amiram Eldar, <a href="/A141229/b141229.txt">Table of n, a(n) for n = 1..10000</a> %t A141229 r[n_] := EulerPhi[n]/MultiplicativeOrder[2, n]; Select[Range[5000], Total@(r /@ Divisors[#]) - 1 == 3 &] (* _Amiram Eldar_, Sep 12 2019 *) %o A141229 (PARI) a006694(n)=sumdiv(2*n+1, d, eulerphi(d)/znorder(Mod(2, d))) - 1; %o A141229 isok(n) = (n % 2) && (a006694((n-1)/2) == 3); \\ _Michel Marcus_, Feb 08 2016 %Y A141229 Cf. A006694, A002326, A001122, A001133. %K A141229 nonn %O A141229 1,1 %A A141229 _Vladimir Shevelev_, Jun 15 2008 %E A141229 More terms from _Michel Marcus_, Feb 08 2016