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A046351 Palindromic composite numbers with only palindromic prime factors. 5
4, 6, 8, 9, 22, 33, 44, 55, 66, 77, 88, 99, 121, 202, 242, 252, 262, 303, 343, 363, 393, 404, 484, 505, 525, 606, 616, 626, 686, 707, 808, 909, 939, 1111, 1331, 1441, 1661, 1991, 2112, 2222, 2662, 2772, 2882, 3333, 3443, 3773, 3883, 3993, 4224, 4444, 5445 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Michael S. Branicky, Table of n, a(n) for n = 1..10000

FORMULA

(A032350 INTERSECT A033620) MINUS {1}. - R. J. Mathar, Sep 09 2015

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

Cf. A002385, A032350, A033620, A046349, A046350.

Sequence in context: A161600 A032350 A078337 * A161732 A066307 A287198

Adjacent sequences:  A046348 A046349 A046350 * A046352 A046353 A046354

KEYWORD

nonn,base,changed

AUTHOR

Patrick De Geest, Jun 15 1998

STATUS

approved

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Last modified April 20 12:44 EDT 2021. Contains 343135 sequences. (Running on oeis4.)