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Number of distinct prime factors of n-th term of Look and Say Sequence A005150.
7

%I #15 Apr 09 2022 06:37:23

%S 0,1,2,2,2,1,1,4,2,2,4,3,3,5,7,7,7,5

%N Number of distinct prime factors of n-th term of Look and Say Sequence A005150.

%C a(16) >= 5. - _Nathaniel Johnston_, Nov 02 2010

%C a(18) >= 5. - _Giovanni Resta_, May 20 2020

%H Andy Huchala, <a href="/A079562/a079562.txt">Factors of A005150(n)</a>

%F a(n) = A001221(A005150(n)). - _Michel Marcus_, Apr 09 2022

%t s[1]=1; s[n_] := s[n] = FromDigits[ Flatten[{ IntegerDigits@ Length@ #, First@ #} & /@ Split[ IntegerDigits@ s[n-1] ]]]; PrimeNu /@ s /@ Range[15] (* _Giovanni Resta_, May 20 2020 *)

%Y Cf. A001221, A005150, A334132.

%K nonn,base,hard,more

%O 1,3

%A _Joseph L. Pe_, Jan 25 2003

%E a(11)-a(15) from _Nathaniel Johnston_, Nov 02 2010

%E a(16)-a(17) from _Giovanni Resta_, May 20 2020

%E a(18) from _Andy Huchala_, Apr 08 2022