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A046351
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Palindromic composite numbers with only palindromic prime factors.
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5
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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
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OFFSET
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1,1
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LINKS
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FORMULA
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MATHEMATICA
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palQ[n_]:=Reverse[x=IntegerDigits[n]]==x; Select[Range[4, 5500], !PrimeQ[#]&&And@@palQ/@Join[{#}, First/@FactorInteger[#]]&](* Jayanta Basu, Jun 05 2013 *)
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PROG
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(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))
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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