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 A336655 #12 Jul 30 2020 01:57:31 %S A336655 1,3,7,9,11,21,23,31,33,43,47,49,59,63,67,69,71,77,79,83,89,93,99,103, %T A336655 107,121,127,129,131,139,141,147,151,161,167,177,179,191,201,207,211, %U A336655 213,217,223,227,231,233,237,239,249,253,263,267,279,281,283,301,307 %N A336655 Odd numbers k such that the multiplicative order of 2 modulo k is squarefree. %H A336655 Amiram Eldar, <a href="/A336655/b336655.txt">Table of n, a(n) for n = 1..10000</a> %H A336655 Francesco Pappalardi, <a href="https://www.emis.de/journals/NYJM/nyjm/NYJM/j/2003/9-17.html">Square free values of the order function</a>, New York J. Math., Vol. 9 (2003), pp. 331-344. %F A336655 The number of terms not exceeding x is (a + o(1))* x * log(x)^(b-1), where a and b (~ 0.46437) are constants (Pappalardi, 2003). %e A336655 3 is a term since the multiplicative order of 2 modulo 3 is 2 which is squarefree. %t A336655 Select[2 * Range[160] - 1, SquareFreeQ[MultiplicativeOrder[2, #]] &] %o A336655 (PARI) isok(k) = (k % 2) && issquarefree(znorder(Mod(2,k))); \\ _Michel Marcus_, Jul 29 2020 %Y A336655 Cf. A002326, A005117, A049149, A336654, A336656. %K A336655 nonn %O A336655 1,2 %A A336655 _Amiram Eldar_, Jul 28 2020