A104186 Number of distinct prime divisors of numbers from four consecutive concatenated odd numbers.

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

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 * A350399 A347648 A184320

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