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A116505
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Number of distinct prime divisors of the concatenation of 1,...,n.
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18
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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; internal format)
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OFFSET
| 1,2
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COMMENTS
| Dario Alpern's factorization program was used for n > 43.
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LINKS
| D. Alpern, Factorization using the Elliptic Curve Method
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EXAMPLE
| 123456 = 2*2*2*2*2*2*3*643, distinct prime divisors are 2, 3 and 643, hence a(6) = 3.
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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 (grafix(AT)csl.pl), Mar 30 2008
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PROG
| (PARI) {a=""; for(n=1, 43, a=concat(a, n); print1(omega(eval(a)), ", "))}
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CROSSREFS
| Cf. A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138793.
Sequence in context: A094528 A077774 A128219 * A110534 A194340 A194288
Adjacent sequences: A116502 A116503 A116504 * A116506 A116507 A116508
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KEYWORD
| nonn,base
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AUTHOR
| Parthasarathy Nambi (PachaNambi(AT)yahoo.com), Mar 20 2006
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EXTENSIONS
| Edited and extended by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Mar 29 2006
Terms 59-100 from Sean A. Irvine (sairvin(AT)xtra.co.nz), Nov 04 2009
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