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 A067599 Decimal encoding of the prime factorization of n: concatenation of prime factors and exponents. 16
 21, 31, 22, 51, 2131, 71, 23, 32, 2151, 111, 2231, 131, 2171, 3151, 24, 171, 2132, 191, 2251, 3171, 21111, 231, 2331, 52, 21131, 33, 2271, 291, 213151, 311, 25, 31111, 21171, 5171, 2232, 371, 21191, 31131, 2351, 411, 213171, 431, 22111, 3251, 21231 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS If n has prime factorization p_1^e_1 * ... * p_r^e_r with p_1 < ... < p_r, then its decimal encoding is p_1 e_1...p_r e_r. For example, 15 = 3^1 * 5^1, so has decimal encoding 3151. Sequence A068633 is a duplicate, up to a conventional initial term a(1)=11. a(31) = a(177147) = 311. Is there any solution to a(n) = n? - Franklin T. Adams-Watters, Dec 18 2006 The earliest duplicate is a(223) = 2231 = a(12). There is no fixed point below 3*10^6. - M. F. Hasler, Oct 06 2013 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 2..10000 EXAMPLE The prime factorization of 24 = 2^3 * 3^1 has corresponding encoding 2331. So a(24) = 2331. a(42) = 213171 since 42 = 2^1*3^1*7^1. - Amarnath Murthy, Feb 27 2002 MAPLE with(ListTools): with(MmaTranslator[Mma]): seq(FromDigits(FlattenOnce(ifactors(n)[2])), n=2..46); # Wolfdieter Lang, Aug 16 2014 # second Maple program: a:= n-> parse(cat(map(i-> i[], sort(ifactors(n)[2]))[])): seq(a(n), n=2..60);  # Alois P. Heinz, Mar 16 2018 MATHEMATICA f[n_] := FromDigits[ Flatten[ IntegerDigits[ FactorInteger[ n]]]]; Table[ f[n], {n, 2, 50} ] PROG (PARI) A067599(n)=eval(concat(concat([""], concat(Vec(factor(n)~))~))) \\ - M. F. Hasler, Oct 06 2013 (Haskell) import Data.Function (on) a067599 n = read \$ foldl1 (++) \$    zipWith ((++) `on` show) (a027748_row n) (a124010_row n) :: Integer -- Reinhard Zumkeller, Oct 27 2013 CROSSREFS Cf. A037276, A080670, A112375. Cf. A027748, A124010. Sequence in context: A116116 A079394 A112375 * A261322 A123846 A168000 Adjacent sequences:  A067596 A067597 A067598 * A067600 A067601 A067602 KEYWORD base,easy,nonn AUTHOR Joseph L. Pe, Jan 31 2002 EXTENSIONS Edited by Robert G. Wilson v, Feb 02 2002 Merged contributions from A068633 to here, and minor edits by M. F. Hasler, Oct 06 2013 STATUS approved

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Last modified December 16 12:59 EST 2018. Contains 318162 sequences. (Running on oeis4.)