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A050677 Number of prime factors of concatenation of numbers from n down to 1, with multiplicity. 8
1, 2, 2, 2, 3, 2, 2, 4, 5, 3, 2, 3, 3, 4, 6, 4, 7, 10, 4, 5, 4, 5, 4, 5, 6, 9, 9, 5, 7, 8, 3, 6, 5, 7, 9, 8, 4, 3, 6, 5, 8, 6, 3, 8, 7, 5, 7, 7, 3, 6, 3, 7, 12, 14, 3, 5, 4, 6, 3, 3, 5, 9, 6, 6 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Strictly speaking a(1) = 0.

Smallest number not yet factored is 656463...4321.

LINKS

Table of n, a(n) for n=1..64.

P. De Geest, Reversed Smarandache Concatenated Numbers, Prime factors from n down to 1

C. Rivera, Primes by Listing

M. Fleuren, Factors and primes of Smarandache sequences.

M. Fleuren, Smarandache Factors and Reverse factors

EXAMPLE

21 = 3*7 so a(2) = 2; 321 = 3*107 so a(3) =2; 4321 = 29*149 so a(4) = 2; etc.

MATHEMATICA

Join[{1}, Table[PrimeOmega[FromDigits[Flatten[IntegerDigits[Range[i, 1, -1]]]]], {i, 2, 36}]] (* Jayanta Basu, May 30 2013 *)

CROSSREFS

Cf. A000422, A046460, A050679-A050682.

Sequence in context: A227911 A325783 A048288 * A058013 A223934 A237531

Adjacent sequences:  A050674 A050675 A050676 * A050678 A050679 A050680

KEYWORD

nonn,base,hard

AUTHOR

Patrick De Geest, Aug 15 1999.

STATUS

approved

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Last modified June 24 16:48 EDT 2019. Contains 324325 sequences. (Running on oeis4.)