

A104517


Number of distinct prime divisors of 55...1 (with n 5s).


4



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

1,1


COMMENTS

Number of distinct prime factors of (10^(n + 1)  1)*5/9  4.  Stefan Steinerberger, Mar 06 2006


LINKS

Amiram Eldar, Table of n, a(n) for n = 1..200


FORMULA

a(n) = A001221(A173804(n+1)).  Amiram Eldar, Jan 24 2020


EXAMPLE

The number of distinct prime divisors of 51 is 2 which is the first term in the sequence.
The number of distinct prime divisors of 551 is 2 which is the second term in the sequence.
The number of distinct prime divisors of 5551 is 3 which is the third term in the sequence.


MAPLE

f:= n > nops(numtheory:factorset( (10^(n + 1)  1)*5/9  4)):
map(f, [$1..92]); # Robert Israel, Mar 08 2018


MATHEMATICA

Table[Length[FactorInteger[(10^(n + 1)  1)*5/9  4]], {n, 1, 50}] (* Stefan Steinerberger, Mar 06 2006 *)


PROG

(MAGMA) [#PrimeDivisors((10^(n+1)1)*5 div 94): n in [1..80]]; // Vincenzo Librandi, Mar 09 2018
(PARI) a(n) = omega((10^(n + 1)  1)*5/9  4); \\ Michel Marcus, Mar 09 2018


CROSSREFS

Cf. A001221, A056684 (a(n)=1), A104484, A173804.
Sequence in context: A214861 A037914 A073813 * A098397 A278744 A082091
Adjacent sequences: A104514 A104515 A104516 * A104518 A104519 A104520


KEYWORD

nonn,base


AUTHOR

Parthasarathy Nambi, Apr 19 2005


EXTENSIONS

More terms from Stefan Steinerberger, Mar 06 2006
a(51)a(92), and offset corrected, by Robert Israel, Mar 08 2018


STATUS

approved



