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This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A359487 a(n) is the smallest start of a run of 2 or more integers having a prime factor greater than n.

Original entry on oeis.org

2, 5, 10, 10, 13, 13, 22, 22, 22, 22, 37, 37, 37, 37, 37, 37, 37, 37, 46, 46, 46, 46, 58, 58, 58, 58, 58, 58, 61, 61, 73, 73, 73, 73, 73, 73, 82, 82, 82, 82, 106, 106, 106, 106, 106, 106, 106, 106, 106, 106, 106, 106, 157, 157, 157, 157, 157, 157, 157, 157, 157, 157, 157, 157, 157, 157, 157
Offset: 1

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Author

Thomas Garrison, Jan 02 2023

Keywords

Comments

Each term is a prime or one less than a prime.
Each even term is twice an odd prime (except for a(1)=2).
Each prime term is of the form 2p-1 where p is prime.

Examples

			For n=5, a(5) = 13 since the two numbers 13 and 14=2*7 both have a prime factor > n.

Crossrefs

Cf. A006530 (gpf), A359488 (run lengths).
Cf. A327909.

Programs

  • PARI
    gpf(n) = vecmax(factor(n)[,1]); \\ A006530
a(n) = my(k=2); while(!((gpf(k)>n) && (gpf(k+1)>n)), k++); k; \\ Michel Marcus, Jan 10 2023

Formula

Conjecture: a(n) ~ 2*n.
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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