This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
a(4) = 88 = 2*2*2*11. a(5) = 252 = 2*2*3*3*7.
a(4) = 44 because 44 is a palindrome with exactly 4 palindromic divisors other than itself and 1, namely 2, 4, 11 and 22, and no smaller palindrome works.
ispali:= proc(n) rev(n) = n end proc:
g:= proc(x) nops(select(ispali,numtheory:-divisors(x) minus {1,x})) end proc:
F:= proc(m)
local x1,x2,x3;
if m::even then
[seq(seq(rev(x1) + 10^(m/2)*x1, x1 = 10^(m/2-1) .. 10^(m/2)-1))]
else
[seq(seq(rev(x1) + 10^((m-1)/2)*x2 + 10^((m+1)/2)*x1,x2=0..9),x1=10^((m-1)/2-1)..10^((m-1)/2)-1)];
fi
end proc:
N:= 50: # for a(0) .. a(N)
V:= Array(0..N): count:= 0:
for d from 1 while count