A125025 Lengths of rows in A124570.

3, 8, 3, 8, 3

Offset: 1

Author

Jonathan Vos Post, Nov 15 2006

Keywords

• nonn
• hard
• more

Comments

This sequence is to A124570 as A123556 is to A124064.

a(n) is at most A053669(n)^2, with equality if and only if A053669(n)^2 is the first semiprime in the corresponding arithmetic progression. - Charlie Neder, Jan 10 2019

By subsampling a given arithmetic progression with k terms and distance d one may generate an arithmetic progression of a larger distance d*b, b=1,2,3...., with 1+(k-1)/b terms: a(b*n) >= 1+floor( (a(n)-1)/b ), b=1,2,3..... - R. J. Mathar, Aug 02 2021

18 <= a(6) <= 24. - Jinyuan Wang, Aug 06 2021

a(12) >= 17. a(18) >= 18. a(24) >= 18. a(30) >= 21. a(36) >= 19. a(42) >= 20. a(6006) >= 24 (starting 652744562555081). Hugo van der Sanden, Aug 14 2021

Crossrefs

Cf. A001358, A123556, A124064, A124570, A091016 (for n=6).