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 A076771 Even numbers n representable as the sum of two non-coprime odd composites. 1
 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 (list; graph; refs; listen; history; text; internal format)
 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 Cf. A161962. Sequence in context: A076770 A105679 A160810 * A179014 A105093 A334015 Adjacent sequences: A076768 A076769 A076770 * A076772 A076773 A076774 KEYWORD nonn,easy AUTHOR Jon Perry, Nov 14 2002 EXTENSIONS Offset corrected by Arkadiusz Wesolowski, Aug 08 2011 STATUS approved

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Last modified September 23 14:27 EDT 2023. Contains 365551 sequences. (Running on oeis4.)