A355299 Largest prime factor of n-th term in Look and Say sequence A005150, with a(1)=1.

1, 11, 7, 173, 10111, 312211, 13112221, 2909, 5578070441, 489923144699, 76572179303098543109, 244020609982169, 46889682313579293049990557739475858123, 213414262009265690085197238570402233414850657035591, 323082514382425741194809828536919444925509282219

Offset: 1

Author

Bernard Schott, Jun 27 2022

Keywords

• nonn
• base

Comments

The terms in A005150 that are known to be primes are a(2) = 11, a(6) = 312211 and a(7) = 13112221 (A100108).

The corresponding smallest prime factor is A334132(n).

Examples

			A005150(7) = 13112221 is prime and a(7) = 13112221.
A005150(8) = 1113213211 = 11 * 19 * 1831 * 2909, hence a(8) = 2909.
		

Links

• Wikipedia, Look-and-say sequence.

Crossrefs

Cf. A005150, A006530, A079562, A100108, A334132.

Formula

a(n) = A006530(A005150(n)).