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 A055079 Smallest number with exactly n nonprime divisors. 9
 1, 4, 8, 12, 30, 24, 36, 48, 60, 72, 2048, 192, 120, 216, 180, 288, 240, 432, 576, 420, 360, 864, 1296, 900, 960, 1728, 720, 840, 1080, 3456, 9216, 1260, 1440, 6912, 34359738368, 1680, 2160, 10368, 2880, 15552, 15360, 3600, 4620, 2520, 4320, 31104 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n)<=2^n; see A057838 for the indices n where a(n)=2^n. LINKS Ray Chandler, Table of n, a(n) for n=1..4438 FORMULA a(n)=Min{k; A000005(k)-A001221(k)=A033273(k)=n} EXAMPLE a(5) = 30 because it is the first integer which has five nonprime divisors (1, 6, 10, 15 and 30; the divisors 2, 3 and 5 are prime). a(35) = 2^35 = 34359738368. a(71) = 2^71 = 2361183241434822606848. a(191) = 2^191 = 3138550867693340381917894711603833208051177722232017256448. MATHEMATICA a = Table[0, {100} ]; Do[ c = Count[ PrimeQ[ Divisors[ n ] ], False]; If[ c < 101 && a[[ c ]] == 0, a[[ c ]] = n], {n, 2, 10077696} ]; PROG (PARI) sme(n) = {k = 1; while (sumdiv(k, d, ! isprime(d)) != n, k++); k; } \\ Michel Marcus, Dec 13 2013 (Haskell) a055079 n = head [x | x <- [1..], a033273 x == n] -- Reinhard Zumkeller, Dec 16 2013 CROSSREFS Cf. A001221, A001222, A058060, A058061, A000005, A033273, A057838. Sequence in context: A233341 A102110 A302829 * A081833 A035403 A050908 Adjacent sequences:  A055076 A055077 A055078 * A055080 A055081 A055082 KEYWORD nonn,nice AUTHOR Labos Elemer, Jun 13 2000 EXTENSIONS More terms from Robert G. Wilson v, Nov 20 2000 Edited by Ray Chandler, Aug 12 2010 STATUS approved

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Last modified April 1 00:35 EDT 2020. Contains 333152 sequences. (Running on oeis4.)