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A104660 Number of distinct prime divisors of 44...443 (with n 4s). 2
1, 1, 2, 2, 1, 3, 3, 1, 2, 2, 1, 2, 2, 3, 3, 3, 3, 3, 4, 3, 3, 6, 3, 4, 3, 3, 6, 4, 1, 5, 1, 4, 3, 5, 3, 6, 4, 2, 6, 2, 2, 3, 5, 3, 4, 4, 4, 2, 2, 4, 4, 3, 4, 5, 6, 3, 3, 5, 2, 4, 3, 5, 4, 4, 3, 6, 4, 3, 6, 6, 4, 5, 4, 2, 4, 5, 2, 4, 5, 6, 4, 4, 3, 6, 5, 4, 5 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..199

FORMULA

a(n) = A001221(A173770(n+1)). - Amiram Eldar, Jan 25 2020

EXAMPLE

The number of distinct prime divisors of 43 is 1 (prime).

The number of distinct prime divisors of 443 is 1 (prime).

The number of distinct prime divisors of 4443 is 2.

MAPLE

A104660 := proc(n) x := [3, seq(4, k=1..n)] ; add(op(i, x)*10^(i-1), i=1..nops(x)) ; numtheory[factorset](%) ; nops(%) ; end proc:

seq(A104660(n), n=1..45) ; # R. J. Mathar, Aug 23 2011

MATHEMATICA

Table[PrimeNu[FromDigits[Join[Table[4, {n}], {3}]]], {n, 50}] (* Alonso del Arte, Aug 23 2011 *)

Table[PrimeNu[FromDigits[PadLeft[{3}, n, 4]]], {n, 2, 70}] (* Harvey P. Dale, Aug 22 2016 *)

CROSSREFS

Cf. A001221, A104518, A173770.

Sequence in context: A104469 A144112 A178568 * A212125 A282936 A220073

Adjacent sequences:  A104657 A104658 A104659 * A104661 A104662 A104663

KEYWORD

nonn,base

AUTHOR

Parthasarathy Nambi, Apr 21 2005

EXTENSIONS

More terms from R. J. Mathar and Alonso del Arte, Aug 23 2011

More terms from Amiram Eldar, Jan 25 2020

STATUS

approved

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Last modified September 26 16:43 EDT 2020. Contains 337374 sequences. (Running on oeis4.)