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A048288 Number of prime factors counted with multiplicity of the reverse concatenation of numbers from 1 to n. 11
0, 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, 7, 7, 4, 8, 8, 4, 9, 5, 7, 8, 10, 3, 7, 6, 4, 9, 10, 1, 3, 8, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
Carlos Rivera, Puzzle 8. Primes by Listing, The Prime Puzzles and Problems Connection.
FORMULA
a(n) = A001222(A000422(n)). - Michel Marcus, Jun 14 2021
EXAMPLE
21 = 3*7 so a(2) = 2; 321 = 3*107 so a(3) = 2; 4321 = 29*149 so a(4) = 2; etc.
a(1)=0 since 1 has no prime factors.
MATHEMATICA
Join[{0}, Table[PrimeOmega[FromDigits[Flatten[IntegerDigits[Range[i, 1, -1]]]]], {i, 2, 36}]] (* Jayanta Basu, May 30 2013 *)
CROSSREFS
Sequence in context: A284565 A227911 A325783 * A050677 A058013 A223934
KEYWORD
nonn,base
AUTHOR
Paul Jasper (jasperpaul(AT)hotmail.com)
EXTENSIONS
Offset and a(19) corrected and more terms from Sean A. Irvine, Jun 13 2021
Edited by N. J. A. Sloane, Sep 04 2021
STATUS
approved

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Last modified March 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)