OFFSET
1,1
EXAMPLE
a(1) = 4 = 2*2 has 1 distinct prime factor and 22 is palindromic.
a(2) = 46 = 23*2 has 2 distinct prime factors and 232 is palindromic.
a(3) = 138 = 23*3*2 has 3 distinct prime factors and 2332 is palindromic.
a(4) = 690 = 23*5*3*2 has 4 distinct prime factors and 23532 is palindromic.
a(5) = 197890 = 257*11*7*5*2 has 5 distinct prime factors and 25711752 is palindromic.
a(6) = 5444670 = 2357*11*7*5*3*2 has 6 distinct prime factors and 2357117532 is palindromic.
a(7) = 156719940 = 223*53*17*13*5*3*2*2 has 7 distinct prime factors and 2235317135322 is palindromic.
a(8) = 4941906970 = 257*113*17*13*11*7*5*2 has 8 distinct prime factors and 257113171311752 is palindromic.
a(9) = 135969743910 = 2357*113*17*13*11*7*5*3*2 has 9 distinct prime factors and 23571131713117532 is palindromic.
a(10) = 121470424854870 = 2357*317*113*31*17*13*7*5*3*2 has 10 distinct prime factors and 23573171133117137532 is palindromic.
MAPLE
with(numtheory): T:=proc(w) local x, y, z; x:=0; y:=w; for z from 1 to ilog10(w)+1 do x:=10*x+(y mod 10); y:=trunc(y/10); od; x; end;
P:=proc(q) local a, b, c, i, j, k, n; c:=1; for j from 1 to q do for n from c to q do
if not isprime(n) then a:=ifactors(n)[2]; b:=[]; if nops(a)=j then for k from 1 to nops(a) do
for i from 1 to a[k][2] do b:=[op(b), a[k][1]]; od; od; b:=sort(b); a:=b[nops(b)];
for k from nops(b)-1 by -1 to 1 do a:=a*10^(ilog10(b[k])+1)+b[k]; od;
if T(a)=a then c:=n; print(n); break; fi; fi; fi; od; od; end: P(10^9);
CROSSREFS
KEYWORD
nonn,base,hard,more
AUTHOR
Paolo P. Lava, Jul 06 2016
EXTENSIONS
a(7)-a(9) from Giovanni Resta
Name clarified by Pontus von Brömssen, Oct 04 2025
a(10) from Michael S. Branicky, Oct 04 2025
a(11)-a(15) from Max Alekseyev, Mar 21 2026
STATUS
approved