A046053 Total number of prime factors of the repunit R(n) = (10^n-1)/9.

0, 1, 2, 2, 2, 5, 2, 4, 4, 4, 2, 7, 3, 4, 6, 6, 2, 9, 1, 7, 7, 7, 1, 10, 5, 6, 7, 8, 5, 13, 3, 11, 6, 6, 7, 12, 3, 3, 6, 11, 4, 15, 4, 11, 10, 6, 2, 13, 4, 10, 8, 9, 4, 14, 8, 12, 6, 8, 2, 20, 7, 5, 14, 15, 7, 15, 3, 10, 6, 12, 2, 18, 3, 7, 12, 6, 8, 16, 6, 15, 13, 7, 3, 22, 7, 8, 10, 15, 5

Offset

1,3

Links

Max Alekseyev, Table of n, a(n) for n = 1..352 (first 322 terms from Ray Chandler)

Eric Weisstein's World of Mathematics, Repunit.

Formula

a(n) = A001222(A002275(n)). - Ray Chandler, Apr 22 2017

a(n) = A057951(n) - 2. - Ray Chandler, Apr 24 2017

Example

R(6) = 111111 = (3) (7) (11) (13) (37), so a(6) = 5.

Mathematica

Table[PrimeOmega[(10^n - 1)/9], {n, 60}] (* Michael De Vlieger, Apr 29 2015 *)

Prog

(PARI) a(n)=bigomega(10^n\9) \\ Charles R Greathouse IV, Apr 29 2015

Crossrefs

Cf. A001222, A002275, A057951. For the number of distinct prime factors see A095370.

Sequence in context: A183380 A260587 A095370 * A368303 A368306 A368302

Adjacent sequences: A046050 A046051 A046052 * A046054 A046055 A046056

Keyword

nonn

Author

Eric W. Weisstein

Status

approved