A161562 Even numbers n such that { n-p ; p prime, 2 < p < n/2 } contains at least twice as many primes as composites.

2, 4, 6, 8, 10, 16, 18, 20, 22, 24, 36, 60, 84, 90, 114, 120, 210, 420

Offset

1,1

Comments

It seems that this sequence is finite, and that 420 is the largest term. [M. F. Hasler, Nov 11 2009]

Links

Table of n, a(n) for n=1..18.

Example

16-3=13,16-5=11.(primes:2 times) 16-7=9.(composite:1 time);
24-5=19,24-7=17,24-11=13.(primes:3 times) 24-3=21.(composite:1 time);
90-3=87,90-7=83,90-11=79,90-17=73,90-19-71,90-23=67,90-29=61,90-31=59,90-37=53,90-43=47.(primes:10 times) 90-5=85,90-13=77,90-41=49.(composite:3 times),..

Prog

(PARI) {for(n=1, 1e6, my(s=0); forprime( p=3, n-1, s+=if( isprime(2*n-p), 1, -2)); s>=0 & print1(2*n", "))} \\ M. F. Hasler, Nov 11 2009

Crossrefs

Sequence in context: A338738 A345986 A226809 * A333019 A102470 A057195

Adjacent sequences: A161559 A161560 A161561 * A161563 A161564 A161565

Keyword

nonn,fini,full

Author

Vladimir Joseph Stephan Orlovsky, Jun 13 2009

Extensions

Reworded definition and initial terms added by M. F. Hasler, Nov 11 2009

Definition reworded by Harvey P. Dale, Sep 17 2023

Status

approved