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

%I A076771 #22 Jan 21 2022 23:29:00
%S A076771 18,24,30,36,40,42,48,50,54,56,60,66,70,72,78,80,84,88,90,96,98,100,
%T A076771 102,104,108,110,112,114,120,126,130,132,136,138,140,144,150,152,154,
%U A076771 156,160,162,168,170,174,176,180,182,184,186,190,192,196,198,200,204
%N A076771 Even numbers n representable as the sum of two non-coprime odd composites.
%C A076771 It is conjectured that there is no N such that for all n > N, every even number is represented.
%C A076771 The conjecture is true since 2p, p prime, is never a member of this sequence. - _Charles R Greathouse IV_, Aug 08 2011
%C A076771 An equivalent definition of this sequence: even numbers n such that phi(n) < (n-4)/2. - _Arkadiusz Wesolowski_, Aug 08 2011
%C A076771 Also: products of an even number >= 6 and an odd number >= 3. - _Charles R Greathouse IV_, Aug 08 2011
%H A076771 Arkadiusz Wesolowski, <a href="/A076771/b076771.txt">Table of n, a(n) for n = 1..1000</a>
%e A076771 40 = 5*(3 + 5).
%o A076771 (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
%o A076771 (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
%Y A076771 Cf. A161962.
%K A076771 nonn,easy
%O A076771 1,1
%A A076771 _Jon Perry_, Nov 14 2002
%E A076771 Offset corrected by _Arkadiusz Wesolowski_, Aug 08 2011