A104543 - OEIS

A104543

Number of distinct prime divisors of 55...559 (with n 5s).

1, 2, 3, 2, 2, 3, 1, 2, 4, 3, 1, 3, 3, 2, 4, 4, 1, 3, 3, 2, 4, 4, 4, 5, 1, 5, 4, 5, 4, 5, 1, 2, 4, 5, 5, 4, 2, 2, 3, 4, 3, 4, 4, 3, 5, 2, 5, 5, 3, 3, 6, 4, 2, 5, 4, 6, 2, 5, 4, 3, 4, 4, 6, 5, 5, 7, 3, 5, 5, 3, 4, 6, 5, 8, 3, 5, 5, 5, 2, 4, 4, 3, 4, 5, 3, 7, 6

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OFFSET

1,2

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..202

FORMULA

a(n) = A001221((31+50*10^n)/9). - R. J. Mathar, Aug 24 2011

EXAMPLE

The number of distinct prime divisors of 59 is 1 (prime).

The number of distinct prime divisors of 559 is 2.

The number of distinct prime divisors of 5559 is 3.

MAPLE

A104543 := proc(n) local x ; x := [9, seq(5, k=1..n)] ; add(op(i, x)*10^(i-1), i=1..nops(x)) ; numtheory[factorset](%) ; nops(%) ; end proc: # R. J. Mathar, Aug 24 2011

MATHEMATICA

Table[PrimeNu[(50*10^n + 31)/9], {n, 0, 50}] (* G. C. Greubel, May 10 2017 *)

Table[PrimeNu[FromDigits[PadLeft[{9}, n, 5]]], {n, 2, 90}] (* Harvey P. Dale, Apr 22 2020 *)

CROSSREFS

Cf. A104484, A104483.

Sequence in context: A270026 A340703 A128049 * A054988 A143393 A269111

Adjacent sequences: A104540 A104541 A104542 * A104544 A104545 A104546

KEYWORD

nonn,base

AUTHOR

Parthasarathy Nambi, Apr 20 2005

EXTENSIONS

More terms from Amiram Eldar, Jan 25 2020

STATUS

approved