OFFSET
1,1
LINKS
Michael S. Branicky, Table of n, a(n) for n = 1..10000
FORMULA
MATHEMATICA
palQ[n_]:=Reverse[x=IntegerDigits[n]]==x; Select[Range[4, 5500], !PrimeQ[#]&&And@@palQ/@Join[{#}, First/@FactorInteger[#]]&](* Jayanta Basu, Jun 05 2013 *)
PROG
(Python)
from itertools import product
from sympy import isprime, primefactors as pf
def pal(n): s = str(n); return s == s[::-1]
def palsthru(maxdigits):
midrange = [[""], [str(i) for i in range(10)]]
for digits in range(1, maxdigits+1):
for p in product("0123456789", repeat=digits//2):
left = "".join(p)
if len(left) and left[0] == '0': continue
for middle in midrange[digits%2]: yield int(left+middle+left[::-1])
def okpal(p): return p > 3 and not isprime(p) and all(pal(f) for f in pf(p))
print(list(filter(okpal, palsthru(4)))) # Michael S. Branicky, Apr 06 2021
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Patrick De Geest, Jun 15 1998
STATUS
approved