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 A028868 #35 Sep 04 2024 08:47:06 %S A028868 2,3,29,31 %N A028868 Primes that when squared give numbers with digits in nonascending order. %C A028868 No other solutions below 2*10^9 (probably finite). - Dec 15 1999 %C A028868 No other solutions below 10^20. - _David A. Corneth_, Oct 28 2023, recomputed after a remark from Max Alekseyev, _David A. Corneth_, Aug 20 2024 %C A028868 Primes p such that p^2 is in A062826. - _Max Alekseyev_, Aug 18 2024 %H A028868 David A. Corneth, <a href="/A028868/a028868_1.gp.txt">PARI program</a> %e A028868 From _David A. Corneth_, Oct 28 2023: (Start) %e A028868 31 is in the sequence as 31 is prime and 31^2 = 961 which has its digits in nonascending order. %e A028868 2979 is not in the sequence even though 2979^2 = 8874441 does have digits in nonascending order but 2979 = 3^2 * 331 is not prime. (End) %o A028868 (PARI) is(n) = my(d = digits(n^2)); d == vecsort(d,,4) && isprime(n) \\ _David A. Corneth_, Oct 28 2023 %o A028868 (PARI) \\ see link for a faster program %Y A028868 Cf. A028869, A028865, A028866, A062826. %K A028868 nonn,base,hard,more %O A028868 1,1 %A A028868 _Patrick De Geest_ %E A028868 Name clarified by _Jon E. Schoenfield_, Oct 27 2023