A104377 - OEIS

%I #11 Jan 27 2020 08:27:42

%S 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,

%T 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,

%U 2,2,6,3,3,4,3,3,3,3,3,3,3,5,3,4,4,4,5

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

%H Amiram Eldar, <a href="/A104377/b104377.txt">Table of n, a(n) for n = 1..10000</a>

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

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

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

%p read("transforms") :

%p 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

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

%Y Cf. A001221, A104186.

%K nonn,base

%O 1,1

%A _Parthasarathy Nambi_, Apr 16 2005

%E Offset corrected and more terms added by _Amiram Eldar_, Jan 27 2020