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

1,2

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).

Links

Table of n, a(n) for n=1..15.

Wikipedia, Look-and-say sequence.

Formula

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

Example

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

Crossrefs

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

Sequence in context: A060954 A350214 A038321 * A298438 A262866 A002749

Adjacent sequences: A355296 A355297 A355298 * A355300 A355301 A355302

Keyword

nonn,base

Author

Bernard Schott, Jun 27 2022

Status

approved