OFFSET
1,1
COMMENTS
From Robert Israel, May 16 2018: (Start)
Palindromes m such that 4*m - 27 is a square.
Each term has an odd number of digits and ends in 3, 7 or 9.
Contains 9*(1+10^k+10^(2*k)) for each k>=1. (End)
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..45
P. De Geest, Palindromic Quasi_Over_Squares of the form n^2+(n+X)
MAPLE
R[1]:= [1, 3, 5, 7, 9]: X[1]:= R[1]:
for k from 2 to 6 do
R[k]:= map(t -> seq(10^(k-1)*j+t, j=0..9), R[k-1]);
X[k]:= map(t -> seq(j+10*t, j=0..9), X[k-1])
od:
Res:= 7, 9:
for k from 1 to 6 do
for j from 1 to 5*10^(k-1) do
r:= 10^(k+1)*X[k][j]+R[k][j];
for y from 0 to 9 do
if issqr(4*(r+10^k*y)-27) then
x:= r+10^k*y;
Res:= Res, x;
fi
od od od:
Res; # Robert Israel, May 16 2018
CROSSREFS
KEYWORD
nonn,base
AUTHOR
EXTENSIONS
More terms from Giovanni Resta, Aug 28 2018
STATUS
approved