OFFSET
1,1
COMMENTS
It is conjectured that there is no N such that for all n > N, every even number is represented.
The conjecture is true since 2p, p prime, is never a member of this sequence. - Charles R Greathouse IV, Aug 08 2011
An equivalent definition of this sequence: even numbers n such that phi(n) < (n-4)/2. - Arkadiusz Wesolowski, Aug 08 2011
Also: products of an even number >= 6 and an odd number >= 3. - Charles R Greathouse IV, Aug 08 2011
LINKS
Arkadiusz Wesolowski, Table of n, a(n) for n = 1..1000
EXAMPLE
40 = 5*(3 + 5).
PROG
(PARI) upTo(lim)=my(v=List()); forstep(a=6, lim\3, 2, forstep(b=3, lim\a, 2, listput(v, a*b))); vecsort(Vec(v), , 8) \\ Charles R Greathouse IV, Aug 08 2011
(PARI) upTo(lim)=my(v=List(), p=7, m); forprime(q=8, lim\2, forstep(n=p+2, q-2, 2, m=n; while((m<<=1)<=lim, listput(v, m))); p=q); forstep(n=2*p+4, lim, 4, listput(v, n)); forprime(p=3, lim>>3, m=p<<3; while(m<=lim, listput(v, m); m<<=1)); vecsort(Vec(v)) \\ Charles R Greathouse IV, Aug 08 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jon Perry, Nov 14 2002
EXTENSIONS
Offset corrected by Arkadiusz Wesolowski, Aug 08 2011
STATUS
approved