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A105194
Number of distinct prime factors of the concatenation of two consecutive odd numbers.
0
1, 2, 1, 2, 2, 2, 2, 2, 3, 1, 2, 1, 1, 4, 2, 1, 3, 1, 2, 2, 2, 2, 2, 2, 2, 3, 1, 1, 3, 1, 1, 2, 2, 2, 3, 3, 2, 3, 2, 2, 3, 2, 2, 3, 2, 1, 2, 2, 2, 2, 1, 2, 2, 2, 1, 3, 1, 2, 4, 2, 2, 2, 2, 2, 3, 2, 3, 2, 3, 1, 2, 1, 1, 3, 2, 1, 2, 1, 3, 3, 1, 2, 3, 3, 1, 4, 2, 2, 3, 1, 1, 2, 3, 3, 2, 1, 2, 4, 4, 2, 2, 1, 2, 3, 1
OFFSET
1,2
COMMENTS
Each odd number is used only once, i.e., although (1,3) and (5,7) are both treated as two consecutive odd numbers, (3,5) and (7,9) are not. [From Harvey P. Dale, Jul 13 2011]
EXAMPLE
a(1) =omega(13) = 1; a(2) = omega(57) = 2; a(3) = omega(911) = 1.
MATHEMATICA
f[n_]:=PrimeNu[FromDigits[Flatten[IntegerDigits/@{First[n], Last[n]}]]]; f/@Partition[Range[1, 421, 2], 2] (* _Harvey P. Dale_, Jul 13 2011 *)
PROG
(PARI) a(n)=omega(eval(Str(4*n-3, 4*n-1)))
CROSSREFS
Sequence in context: A193386 A068212 A323015 * A008335 A106031 A055175
KEYWORD
nonn,base
AUTHOR
_Parthasarathy Nambi_, Apr 11 2005
EXTENSIONS
Extended, corrected, and edited by _Charles R Greathouse IV_, Apr 27 2010
STATUS
approved