A076771 Even numbers n representable as the sum of two non-coprime odd composites.

18, 24, 30, 36, 40, 42, 48, 50, 54, 56, 60, 66, 70, 72, 78, 80, 84, 88, 90, 96, 98, 100, 102, 104, 108, 110, 112, 114, 120, 126, 130, 132, 136, 138, 140, 144, 150, 152, 154, 156, 160, 162, 168, 170, 174, 176, 180, 182, 184, 186, 190, 192, 196, 198, 200, 204

Offset: 1

Author

Jon Perry, Nov 14 2002

Keywords

• nonn
• easy

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

Examples

			40 = 5*(3 + 5).
		

Links

• Arkadiusz Wesolowski, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A161962.

Programs

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

Extensions

Offset corrected by Arkadiusz Wesolowski, Aug 08 2011