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 A308961 #23 Jul 13 2019 11:28:47 %S A308961 2,7,97,997,9997,20247,99997,999997,9999997,99999997,999999997, %T A308961 2224745247,9999999997,99999999997,999999999997,9999999999997, %U A308961 99999999999997,999999999999997,9999999999999997,99999999999999997 %N A308961 Numbers k not divisible by 10 such that k^2 and 2*k are in A046030. %C A308961 10^j - 3 are terms. Most of the terms so far are of the form 10^j - 3. Are there other terms not of this form besides 2, 20247, and 2224745247? %C A308961 If k is a term, then primes of the form k*10^j + 1 for j >= A055642(2*k) are in A308917 and primes of the form 10^j + k for j >= A055642(k^2) are in A308917. %Y A308961 Cf. A046030, A055642, A308917. %K A308961 nonn,base %O A308961 1,1 %A A308961 _Chai Wah Wu_, Jul 04 2019 %E A308961 Edited by _Max Alekseyev_, Jul 13 2019