

A104186


Number of distinct prime divisors of numbers from four consecutive concatenated odd numbers.


2



2, 2, 2, 2, 3, 3, 3, 2, 2, 4, 2, 1, 3, 3, 2, 2, 3, 2, 2, 4, 3, 2, 4, 2, 2, 3, 3, 4, 4, 3, 2, 4, 3, 2, 5, 2, 2, 4, 1, 3, 3, 4, 2, 3, 3, 2, 3, 3, 3, 4, 3, 3, 2, 3, 5, 3, 3, 1, 4, 4, 2, 4, 2, 2, 5, 2, 4, 3, 3, 3, 3, 4, 2, 4, 3, 2, 3, 2, 2, 3, 4, 3, 3, 2, 3, 6, 4
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OFFSET

1,1


COMMENTS

Interestingly, 23252729 is prime.


LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000


EXAMPLE

The number of distinct prime factors of 1357 is 2  the first term in the sequence.
The number of distinct prime factors of 3579 is 2  the second term in the sequence.
The number of distinct prime factors of 57911 is 2  the third term in the sequence.


MATHEMATICA

a[n_] := PrimeNu@ FromDigits @ (Join @@ IntegerDigits /@ (2*n + {1, 1, 3, 5})); Array[a, 100] (* Amiram Eldar, Jan 27 2020 *)


CROSSREFS

Cf. A001221, A104377.
Sequence in context: A194320 A231555 A120425 * A184320 A092363 A133874
Adjacent sequences: A104183 A104184 A104185 * A104187 A104188 A104189


KEYWORD

nonn,base


AUTHOR

Parthasarathy Nambi, Apr 16 2005


EXTENSIONS

Offset corrected and more terms added by Amiram Eldar, Jan 27 2020


STATUS

approved



