A079562 Number of distinct prime factors of n-th term of Look and Say Sequence A005150.

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

Offset: 1

Author

Joseph L. Pe, Jan 25 2003

Keywords

• nonn
• base
• hard
• more

Comments

a(16) >= 5. - Nathaniel Johnston, Nov 02 2010

a(18) >= 5. - Giovanni Resta, May 20 2020

Links

• Andy Huchala, Factors of A005150(n)

Crossrefs

Cf. A001221, A005150, A334132.

Programs

Mathematica

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 *)

Formula

a(n) = A001221(A005150(n)). - Michel Marcus, Apr 09 2022

Extensions

a(11)-a(15) from Nathaniel Johnston, Nov 02 2010

a(16)-a(17) from Giovanni Resta, May 20 2020

a(18) from Andy Huchala, Apr 08 2022