A027716 Numbers k such that k^2 + k + 4 is a palindrome.

0, 1, 20, 200, 219, 261, 2000, 2234, 2551, 2613, 20000, 20604, 200000, 202885, 205704, 218354, 2000000, 2155139, 2490266, 2620486, 20000000, 25882353, 200000000, 205705704, 2000000000, 2094600194, 20000000000, 20102030400, 20349812814, 21572321960

Offset: 1

Author

Patrick De Geest

Keywords

• nonn
• base

Comments

Includes 2*10^k for k>=2. - Robert Israel, Apr 16 2019

Links

• Giovanni Resta, Table of n, a(n) for n = 1..36
• P. De Geest, Palindromic Quasi_Over_Squares of the form n^2+(n+X)

Crossrefs

Cf. A027717, A027689, A027714, A027718.

Programs

Mathematica

palQ[n_] := Block[{d = IntegerDigits[n]}, d == Reverse[d]]; f[n_] := n^2 + n + 4; Select[Range[0, 10^5], palQ@ f@ # &] (* Giovanni Resta, Aug 29 2018 *)
Select[Range[0,3*10^6],PalindromeQ[#^2+#+4]&] (* The program generates the first 20 terms of the sequence. *) (* Harvey P. Dale, Jul 22 2024 *)

Extensions

More terms from Giovanni Resta, Aug 29 2018