A102621 - OEIS

%I #18 Jul 09 2023 09:50:13

%S 0,3,6,5,3,8,10,9,13,11,11,12,13,11,13,10,10,11,13,21,15,14,11,13,17,

%T 7,14,16

%N Number of distinct prime factors of (nonprime A018252(n) concatenated A018252(n) times).

%H Dario A. Alpern, <a href="https://www.alpertron.com.ar/ecm.htm">Factorization using the Elliptic curve method</a>.

%F a(n) = A001221(A102622(n)). - _R. J. Mathar_, Aug 24 2011

%e For n=2, the number of distinct prime factors of 4444 is 3.

%e For n=3, the number of distinct prime factors of 666666 is 6.

%e For n=4, the number of distinct prime factors of 88888888 is 5.

%e For n=5, the number of distinct prime factors of 999999999 is 3.

%p read("transforms") ;

%p A102621 := proc(n) c := A018252(n) ; x := c ; for j from 2 to c do x := digcat2(x,c) ; end do; A001221(x) ; end proc: # _R. J. Mathar_, Aug 24 2011

%t PrimeNu/@(FromDigits/@(Flatten[Table[IntegerDigits[#],#]]&/@Select[ Range[ 40],!PrimeQ[#]&])) (* _Harvey P. Dale_, Sep 03 2018 *)

%Y Cf. A101081.

%K nonn,base,less

%O 1,2

%A _Parthasarathy Nambi_, Jan 31 2005

%E More terms from _Harvey P. Dale_, Sep 03 2018