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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 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 59-100 from Sean A. Irvine, Nov 04 2009 STATUS approved

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Last modified August 23 01:10 EDT 2019. Contains 326211 sequences. (Running on oeis4.)