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A046349
Composite numbers with only palindromic prime factors.
4
4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 27, 28, 30, 32, 33, 35, 36, 40, 42, 44, 45, 48, 49, 50, 54, 55, 56, 60, 63, 64, 66, 70, 72, 75, 77, 80, 81, 84, 88, 90, 96, 98, 99, 100, 105, 108, 110, 112, 120, 121, 125, 126, 128, 132, 135, 140, 144, 147, 150
OFFSET
1,1
LINKS
FORMULA
A033620 INTERSECT A002808. - R. J. Mathar, Sep 09 2015
MAPLE
isA046349 := proc(n)
simplify(isA033620(n) and not isprime(n)) ;
end proc:
for n from 2 to 300 do
if isA046349(n) then
printf("%d, ", n) ;
end if;
end do: # R. J. Mathar, Sep 09 2015
MATHEMATICA
palQ[n_]:=Reverse[x=IntegerDigits[n]]==x; Select[Range[4, 150], !PrimeQ[#]&&And@@palQ/@First/@FactorInteger[#]&] (* Jayanta Basu, Jun 05 2013 *)
Select[Range[200], CompositeQ[#]&&AllTrue[FactorInteger[#][[All, 1]], PalindromeQ]&] (* Harvey P. Dale, May 15 2022 *)
PROG
(Python)
from sympy import isprime, primefactors
def pal(n): s = str(n); return s == s[::-1]
def ok(n): return not isprime(n) and all(pal(f) for f in primefactors(n))
print(list(filter(ok, range(4, 151)))) # Michael S. Branicky, Apr 06 2021
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Patrick De Geest, Jun 15 1998
STATUS
approved