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 A102347 Number of distinct prime factors of 10^n - 1. 2
 1, 2, 2, 3, 3, 5, 3, 5, 3, 5, 3, 7, 4, 5, 6, 7, 3, 8, 2, 8, 7, 7, 2, 10, 6, 7, 5, 9, 6, 13, 4, 12, 6, 7, 8, 11, 4, 4, 6, 12, 5, 14, 5, 11, 9, 7, 3, 13, 5, 11, 8, 10, 5, 12, 9, 13, 6, 9, 3, 20, 8, 6, 13, 16, 8, 14, 4, 11, 6, 13, 3, 17, 4, 8, 12, 7, 9, 15, 7, 16, 10, 8, 4, 21, 8, 9, 10, 15, 6, 21, 13 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Ray Chandler, Table of n, a(n) for n = 1..322 (first 280 terms from Max Alekseyev) FORMULA a(n) = A001221(A002283(n)) = A001221(10^n - 1). a(n) = A001221(R_n) + (n^2 mod 3) = A095370(n) + (n^2 mod 3), where R_n = (10^n-1)/9 = A002275(n). That is, a(n) = A095370(n) for n=3k; otherwise a(n) = A095370(n) + 1. - Lekraj Beedassy, Jun 09 2006 MAPLE A102347 := proc(n)     10^n-1 ;     A001221(%) ; end proc: # R. J. Mathar, Dec 02 2016 MATHEMATICA Table[PrimeNu[10^n-1], {n, 100}] (* The program will take a long time to execute *) (* Harvey P. Dale, Jan 18 2015 *) PROG (PARI) a(n) = omega(10^n-1); \\ Michel Marcus, Apr 22 2017 CROSSREFS Cf. A001221, A002283, A070528. Sequence in context: A079375 A069933 A204987 * A230846 A204908 A340265 Adjacent sequences:  A102344 A102345 A102346 * A102348 A102349 A102350 KEYWORD nonn AUTHOR Jun Mizuki (suzuki32(AT)sanken.osaka-u.ac.jp), Feb 20 2005 STATUS approved

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Last modified September 26 06:16 EDT 2021. Contains 347664 sequences. (Running on oeis4.)