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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 (list; graph; refs; listen; history; text; internal format)
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: A128219 A238969 A238956 * 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 59-100 from Sean A. Irvine, Nov 04 2009

STATUS

approved

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Last modified August 20 15:27 EDT 2017. Contains 290835 sequences.