OFFSET
1,1
COMMENTS
Every palindrome with an even number of digits is divisible by 11 (in base 8) and therefore is composite (not prime). Hence there is no palindromic prime with an even number of digits.
LINKS
Eric Weisstein: Palindromic Prime.
MAPLE
revdigs:= proc(n) local L, i;
L:= convert(n, base, 8);
add(L[-i]*8^(i-1), i=1..nops(L))
end proc:
f:= proc(d) local x, y;
nops(select(isprime, [seq(seq(x*8^(d+1)+y*8^d+revdigs(x), y=0..7), x=8^(d-1)..8^d-1)]));
end proc:
T:= ListTools:-PartialSums([4, op(map(f, [$1..6]))]):
map(t -> (t, t), T); # Robert Israel, Aug 01 2019
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Martin Renner, Apr 15 2006
EXTENSIONS
a(9)-a(22) from Robert Israel, Aug 01 2019, using data from A117786.
STATUS
approved