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 A083830 #9 Jul 20 2020 11:48:05 %S A083830 4,7,22,232,424,454,484,727,757,787,2332,23332,42124,42424,42724, %T A083830 45154,45454,45754,48184,48484,48784,72127,72427,72727,75157,75457, %U A083830 75757,78187,78487,78787,233332,2333332,4212124,4215124,4218124,4242424 %N A083830 Palindromes of the form 3n + 1 where n is also a palindrome: palindromes arising in A083829. %t A083830 Select[3#+1&/@Select[Range[15*10^5],PalindromeQ],PalindromeQ] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jul 20 2020 *) %Y A083830 Cf. A083829. %K A083830 base,nonn %O A083830 1,1 %A A083830 _Amarnath Murthy_ and Meenakshi Srikanth (menakan_s(AT)yahoo.com), May 09 2003 %E A083830 Corrected and extended by _Ray Chandler_, May 21 2003