A082723 - OEIS

%I #9 Aug 11 2024 14:41:34

%S 1,9,111,474,969,6666,18981,67276,4411144,6964696,15444451,57966975,

%T 448707844,460595064,579696975,931929139,994040499,1227667221,

%U 9698998969,61556965516,664248842466,699030030996,99451743334715499

%N Palindromic nonagonal (or 9-gonal or enneagonal) numbers.

%H P. De Geest, <a href="https://www.worldofnumbers.com/nona.htm">Palindromic nonagonals</a>

%t palQ[n_]:=Module[{idn=IntegerDigits[n]},idn==Reverse[idn]]; Select[Table[ (n(7n-5))/2,{n,170000000}],palQ] (* _Harvey P. Dale_, Nov 15 2011 *)

%Y Cf. A001106, A055560.

%K nonn,base

%O 1,2

%A _Patrick De Geest_, Apr 13 2003