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

0, 1, 7, 14, 21, 33, 44, 144, 235, 269, 524, 1123, 1452, 1582, 5412, 8338, 8459, 11063, 11223, 23255, 73491, 145544, 262808, 266737, 281349, 1659022, 2705669, 3504083, 5040882, 7395091, 8308388, 14554452, 85559327, 110651063, 223674495, 277945157, 282442347

Offset: 1

Author

Patrick De Geest

Keywords

• nonn
• base

Links

• Michael S. Branicky, Table of n, a(n) for n = 1..49
• Patrick De Geest, Palindromic Quasipronics of the form n(n+x)
• Erich Friedman, What's Special About This Number? (See entries 1452, 1582, 5412, 8338, 8459.)

Crossrefs

Cf. A028336, A028347, A028556.

Programs

Mathematica

Select[Range[0, 9999], PalindromeQ[#^2 + 4#] &] (* Alonso del Arte, Nov 10 2019 *)

Python

from itertools import count, islice
def ispal(n): s = str(n); return s == s[::-1]
def agen():
    for k in count(0):
        if ispal(k*(k+4)):
            yield k
print(list(islice(agen(), 32))) # Michael S. Branicky, Jan 25 2022

Scala

def palQ(n: Int, b: Int = 10): Boolean = n - Integer.parseInt(n.toString.reverse) == 0
(0 to 9999).filter((n: Int) => palQ(n * n + 4 * n)) // Alonso del Arte, Nov 10 2019

Extensions

a(33) and beyond from Michael S. Branicky, Jan 25 2022