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 A280890 Minimum number k such that n iterations of products of prime factor exponents are required to reduce k to 1. 3
 2, 4, 16, 1296, 9681819840000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS MathOverflow, Product of Exponents of Prime Factorization. EXAMPLE The term a(5) = 9681819840000, which factors as 2^9*3^6*5^4*7^3*11^2, because 9*6*4*3*2 = 1296 = 2^4*3^4 and 4*4 = 16 = 2^4 and 4 = 2^2 and 2 = 2^1 gives 1 in 5 iterations of products of prime exponents -- and no smaller positive integer has this property (see link). MATHEMATICA Table[k = 1; While[Length@ NestWhileList[Times @@ (FactorInteger[#][[All, -1]]) &, k, # > 1 &] - 1 != n, k++]; k, {n, 4}] (* Michael De Vlieger, Jan 25 2017 *) CROSSREFS Cf. A005361. Sequence in context: A152690 A194457 A001128 * A124436 A014221 A249760 Adjacent sequences:  A280887 A280888 A280889 * A280891 A280892 A280893 KEYWORD nonn,hard AUTHOR Rick L. Shepherd, Jan 09 2017 STATUS approved

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Last modified July 10 23:30 EDT 2020. Contains 335600 sequences. (Running on oeis4.)