

A116505


Number of distinct prime divisors of the concatenation of 1,...,n.


18



0, 2, 2, 2, 3, 3, 2, 4, 3, 3, 6, 4, 3, 3, 3, 3, 4, 5, 6, 6, 8, 6, 4, 5, 4, 6, 5, 5, 4, 7, 3, 5, 6, 2, 7, 5, 4, 4, 6, 8, 5, 7, 4, 4, 9, 7, 5, 7, 6, 9, 3, 3, 4, 9, 5, 4, 6, 4, 4, 6, 3, 7, 4, 9, 6, 8, 3, 7, 7, 6, 5, 5, 3, 9, 5, 4, 5, 6, 6, 7, 4, 7, 6, 3, 5, 7, 6, 5, 9, 8, 6, 6, 7, 5, 6, 5, 2, 9, 5, 9
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OFFSET

1,2


COMMENTS

Dario Alpern's factorization program was used for n > 43.


LINKS

Table of n, a(n) for n=1..100.
D. Alpern, Factorization using the Elliptic Curve Method


EXAMPLE

123456 = 2*2*2*2*2*2*3*643, distinct prime divisors are 2, 3 and 643, hence a(6) = 3.


MATHEMATICA

b = {}; a = {}; Do[w = RealDigits[n]; w = First[w]; Do[AppendTo[a, w[[k]]], {k, 1, Length[w]}]; p = FromDigits[a]; m = FactorInteger[p]; AppendTo[b, Length[m]], {n, 1, 20}]; b  Artur Jasinski, Mar 30 2008


PROG

(PARI) {a=""; for(n=1, 43, a=concat(a, n); print1(omega(eval(a)), ", "))}


CROSSREFS

Cf. A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138793.
Sequence in context: A238969 A238956 A295511 * A110534 A194340 A194288
Adjacent sequences: A116502 A116503 A116504 * A116506 A116507 A116508


KEYWORD

nonn,base


AUTHOR

Parthasarathy Nambi, Mar 20 2006


EXTENSIONS

Edited and extended by Klaus Brockhaus, Mar 29 2006
Terms 59100 from Sean A. Irvine, Nov 04 2009


STATUS

approved



