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 A046447 Apart from initial term, composite numbers with property that concatenation of prime factors is a palindrome. 12
 1, 4, 8, 9, 16, 25, 27, 32, 39, 49, 64, 69, 81, 119, 121, 125, 128, 129, 159, 219, 243, 249, 256, 259, 329, 339, 343, 403, 429, 469, 507, 512, 625, 669, 679, 729, 795, 1024, 1207, 1309, 1329, 1331, 1533, 1547, 1587, 1589, 1703, 2023, 2048, 2097, 2187, 2319 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..1000 EXAMPLE E.g., 81 = 3 * 3 * 3 * 3 -> 3333 is palindromic. MATHEMATICA concat[n_]:=Flatten[Table[IntegerDigits[First[n]], {Last[n]}]]; palQ[n_]:= Module[{x=Flatten[concat/@FactorInteger[n]]}, x==Reverse[x]&&!PrimeQ[n]]; Select[Range[2500], palQ] (* Harvey P. Dale, May 24 2011 *) PROG (Haskell) a046447 n = a046447_list !! (n-1) a046447_list = 1 : filter f [1..] where f x = length ps > 1 && ps' == reverse ps' where ps' = concatMap show ps; ps = a027746_row x -- Reinhard Zumkeller, May 02 2014 (Python) from sympy import factorint, isprime A046447_list = [1] for n in range(4, 10**6): ....if not isprime(n): ........s = ''.join([str(p)*e for p, e in sorted(factorint(n).items())]) ........if s == s[::-1]: ............A046447_list.append(n) # Chai Wah Wu, Jan 03 2015 CROSSREFS Cf. A046448, A046449, A046450. Cf. A027746, A018252, A136522, A002113. Sequence in context: A075309 A175031 A052054 * A087244 A080062 A249125 Adjacent sequences: A046444 A046445 A046446 * A046448 A046449 A046450 KEYWORD nonn,nice,base AUTHOR Patrick De Geest, Jul 15 1998 STATUS approved

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Last modified October 4 09:13 EDT 2023. Contains 365873 sequences. (Running on oeis4.)