A105194 Number of distinct prime factors of the concatenation of two consecutive odd numbers.

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]

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