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 A306450 #13 Feb 25 2019 20:51:07 %S A306450 726,1053426,6498426,7912311,8141001,190381521,202730781,283975626, %T A306450 524245326,767159481,1095790641,1620456321,1904467521,2287621281, %U A306450 2700546486,3462782961,4120800321,4928482581,5816852481,5974336401,9313587921,18723332001,21215225361,22073079666,29882080866,30132305841 %N A306450 Non-coprime pseudoprimes to base 3 (A306451) that are not squarefree. %C A306450 Intersection of A306451 and A013929. %C A306450 Terms must be divisible by the square of a Mirimanoff prime p (or base-3 Wieferich prime, A014127) such that the multiplicative order of 3 modulo p is not divisible by 3. So far, the only known Mirimanoff primes are 11 and 1006003. The multiplicative order of 3 modulo 11 is 5, not a multiple of 3, while the multiplicative order of 3 modulo 1006003 is 1006002, which is a multiple of 3. As a result, all known terms are divisible by 3*11^2 = 363. %e A306450 726 is a term because 726 divides 3^726 - 3 and 726 = 2 * 3 * 11^2. %o A306450 (PARI) forstep(n=3, 10^9, 3, if(Mod(3, n)^n==3 && !issquarefree(n), print1(n, ", "))) %Y A306450 Cf. A295740, A244065, A306451, A306452. %K A306450 nonn %O A306450 1,1 %A A306450 _Jianing Song_, Feb 16 2019 %E A306450 More terms from _Jinyuan Wang_, Feb 18 2019