cp's OEIS Frontend

A028555 Numbers k such that k*(k+4) is a palindrome.

%I A028555 #24 Jan 26 2022 02:36:01
%S A028555 0,1,7,14,21,33,44,144,235,269,524,1123,1452,1582,5412,8338,8459,
%T A028555 11063,11223,23255,73491,145544,262808,266737,281349,1659022,2705669,
%U A028555 3504083,5040882,7395091,8308388,14554452,85559327,110651063,223674495,277945157,282442347
%N A028555 Numbers k such that k*(k+4) is a palindrome.
%H A028555 Michael S. Branicky, <a href="/A028555/b028555.txt">Table of n, a(n) for n = 1..49</a>
%H A028555 Patrick De Geest, <a href="http://www.worldofnumbers.com/consemor.htm">Palindromic Quasipronics of the form n(n+x)</a>
%H A028555 Erich Friedman, <a href="https://erich-friedman.github.io/numbers.html">What's Special About This Number?</a> (See entries 1452, 1582, 5412, 8338, 8459.)
%t A028555 Select[Range[0, 9999], PalindromeQ[#^2 + 4#] &] (* _Alonso del Arte_, Nov 10 2019 *)
%o A028555 (Scala) def palQ(n: Int, b: Int = 10): Boolean = n - Integer.parseInt(n.toString.reverse) == 0
%o A028555 (0 to 9999).filter((n: Int) => palQ(n * n + 4 * n)) // _Alonso del Arte_, Nov 10 2019
%o A028555 (Python)
%o A028555 from itertools import count, islice
%o A028555 def ispal(n): s = str(n); return s == s[::-1]
%o A028555 def agen():
%o A028555     for k in count(0):
%o A028555         if ispal(k*(k+4)):
%o A028555             yield k
%o A028555 print(list(islice(agen(), 32))) # _Michael S. Branicky_, Jan 25 2022
%Y A028555 Cf. A028336, A028347, A028556.
%K A028555 nonn,base
%O A028555 1,3
%A A028555 _Patrick De Geest_
%E A028555 a(33) and beyond from _Michael S. Branicky_, Jan 25 2022