A068641 Smallest n-digit palindromic triangular number, or 0 if no such number exists.

1, 55, 171, 3003, 15051, 617716, 1269621, 35133153, 178727871, 1264114621, 13953435931, 0, 1313207023131, 19895044059891, 114401848104411, 1250444114440521, 11121736463712111, 357961407704169753

Offset

1,2

Links

Table of n, a(n) for n=1..18.

P. De Geest, Exhaustive list of Palindromic Triangulars

Example

a(4) = 3003 = 77*78/2 is the smallest 4-digit palindromic triangular number.
a(12) = 0 as no 12-digit palindromic triangular number exists.

Mathematica

With[{trs=Select[Accumulate[Range[10^6]], IntegerLength[#]<12&]}, Table[SelectFirst[trs, IntegerLength[#]==n&&PalindromeQ[#]&], {n, 11}]] (* The program generates the first 11 terms of the sequence. *) (* Harvey P. Dale, Dec 24 2025 *)

Crossrefs

Cf. A068642, A068643, A068644, A000217, A003098, A008509, A008510, A054263.

Sequence in context: A352268 A276050 A256353 * A039781 A135657 A178793

Adjacent sequences: A068638 A068639 A068640 * A068642 A068643 A068644

Keyword

base,nonn

Author

Amarnath Murthy, Feb 28 2002

Extensions

Edited by Patrick De Geest, Mar 24 2002

Status

approved