(cache)A102347

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A102347

Number of distinct prime factors of 10^n - 1.

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 A263027` `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 June 17 01:30 EDT 2018. Contains 305504 sequences. (Running on oeis4.)