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

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Last modified May 5 17:56 EDT 2021. Contains 343572 sequences. (Running on oeis4.)