A028555 - OEIS

%I #24 Jan 26 2022 02:36:01

%S 0,1,7,14,21,33,44,144,235,269,524,1123,1452,1582,5412,8338,8459,

%T 11063,11223,23255,73491,145544,262808,266737,281349,1659022,2705669,

%U 3504083,5040882,7395091,8308388,14554452,85559327,110651063,223674495,277945157,282442347

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

%H Michael S. Branicky, <a href="/A028555/b028555.txt">Table of n, a(n) for n = 1..49</a>

%H Patrick De Geest, <a href="http://www.worldofnumbers.com/consemor.htm">Palindromic Quasipronics of the form n(n+x)</a>

%H 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 Select[Range[0, 9999], PalindromeQ[#^2 + 4#] &] (* _Alonso del Arte_, Nov 10 2019 *)

%o (Scala) def palQ(n: Int, b: Int = 10): Boolean = n - Integer.parseInt(n.toString.reverse) == 0

%o (0 to 9999).filter((n: Int) => palQ(n * n + 4 * n)) // _Alonso del Arte_, Nov 10 2019

%o (Python)

%o from itertools import count, islice

%o def ispal(n): s = str(n); return s == s[::-1]

%o def agen():

%o     for k in count(0):

%o         if ispal(k*(k+4)):

%o             yield k

%o print(list(islice(agen(), 32))) # _Michael S. Branicky_, Jan 25 2022

%Y Cf. A028336, A028347, A028556.

%K nonn,base

%O 1,3

%A _Patrick De Geest_

%E a(33) and beyond from _Michael S. Branicky_, Jan 25 2022