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 A028336 #28 Feb 16 2025 08:32:35 %S A028336 1,2,16,77,538,1621,2457,5291,5313,52008,142401,143498,1610151, %T A028336 1713543,4670028,5218983,15137566,15282411,15814148,47370058,50702751, %U A028336 142594226,166691108,1694576061,2554554552,25541432472,47878213558,77714915542,155482156418 %N A028336 Positive numbers k such that k*(k+1) is a palindrome. %C A028336 For additional terms, see the De Geest link. %H A028336 P. De Geest, <a href="https://www.worldofnumbers.com/consec.htm">Palindromic pronic numbers of the form n(n+1)</a> %H A028336 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PalindromicNumber.html">Palindromic Number.</a> %H A028336 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PronicNumber.html">Pronic Number.</a> %t A028336 Select[Range[500000], PalindromeQ[#(#+1)] &] (* or *) Select[Range[50000], IntegerDigits[#(#+1)] == Reverse[ IntegerDigits[#(#+1)]] &] (* _G. C. Greubel_, Nov 24 2016 *) %o A028336 (PARI) isok(k) = my(d = digits(k*(k+1))); Vecrev(d) == d; \\ _Michel Marcus_, Nov 09 2017 %Y A028336 Cf. A008509, A028337. %K A028336 nonn,base %O A028336 1,2 %A A028336 _Patrick De Geest_ %E A028336 More terms from _Jon E. Schoenfield_, Nov 09 2017