A104377 - OEIS

A104377

Number of distinct prime divisors of numbers derived from three consecutive concatenated odd numbers.

2, 3, 2, 2, 3, 4, 2, 3, 3, 2, 4, 2, 2, 2, 2, 4, 3, 3, 2, 2, 4, 3, 3, 3, 2, 5, 3, 2, 3, 3, 3, 3, 2, 2, 2, 3, 2, 3, 3, 3, 3, 3, 3, 3, 2, 3, 3, 3, 4, 2, 4, 4, 4, 3, 3, 4, 2, 3, 4, 3, 4, 3, 3, 3, 3, 5, 3, 4, 2, 2, 6, 3, 3, 4, 3, 3, 3, 3, 3, 3, 3, 5, 3, 4, 4, 4, 5

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OFFSET

1,1

LINKS

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

EXAMPLE

The number of distinct prime divisors of 135 is 2 - the first term in the sequence.

The number of distinct prime divisors of 357 is 3 - the second term in the sequence.

The number of distinct prime divisors of 579 is 2 - the third term in the sequence.

MAPLE

read("transforms") :

A104377 := proc(n) digcat2(digcat2(2*n+1, 2*n+3), 2*n+5) ; nops(numtheory[factorset](%)) ; end proc: # R. J. Mathar, Feb 03 2011

MATHEMATICA

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

CROSSREFS

Cf. A001221, A104186.

Sequence in context: A079643 A329317 A118480 * A109337 A303539 A303540

Adjacent sequences: A104374 A104375 A104376 * A104378 A104379 A104380

KEYWORD

nonn,base

AUTHOR

Parthasarathy Nambi, Apr 16 2005

EXTENSIONS

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

STATUS

approved