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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 (list; graph; refs; listen; history; text; internal format)
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]

LINKS

Table of n, a(n) for n=1..105.

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

Adjacent sequences:  A105191 A105192 A105193 * A105195 A105196 A105197

KEYWORD

nonn,base

AUTHOR

Parthasarathy Nambi, Apr 11 2005

EXTENSIONS

Extended, corrected, and edited by Charles R Greathouse IV, Apr 27 2010

STATUS

approved

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Last modified December 7 13:08 EST 2021. Contains 349581 sequences. (Running on oeis4.)