

A161562


Even numbers n such that { np ; p prime, 2 < p < n/2 } contains at least twice as much primes than composites.


0



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

163=13,165=11.(primes:2 times) 167=9.(composite:1 time);
245=19,247=17,2411=13.(primes:3 times) 243=21.(composite:1 time);
903=87,907=83,9011=79,9017=73,901971,9023=67,9029=61,9031=59,9037=53,9043=47.(primes:10 times) 905=85,9013=77,9041=49.(composite:3 times),..


PROG

(PARI) {for(n=1, 1e6, my(s=0); forprime( p=3, n1, s+=if( isprime(2*np), 1, 2)); s>=0 & print1(2*n", "))} \\ M. F. Hasler, Nov 11 2009


CROSSREFS

Sequence in context: A177867 A338738 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


STATUS

approved



