cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A205668 Prime numbers that cannot be expressed as the sum of two lesser primes of twin prime pairs + 1 or two greater primes of twin prime pairs - 1.

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%I A205668 #15 Dec 07 2015 01:02:42
%S A205668 2,3,5,97,401,787,907,1117
%N A205668 Prime numbers that cannot be expressed as the sum of two lesser primes of twin prime pairs + 1 or two greater primes of twin prime pairs - 1.
%C A205668 The occurrence of a pair of twin primes in the sequence would be a counterexample to the conjecture in A134143.
%C A205668 There are probably no more terms. As in Goldbach's conjecture, the number of summands increases rapidly. - _Charles R Greathouse IV_, Jan 31 2012
%F A205668 A000040(n) != A001359(j) + A001359(k) + 1 and A000040(n) != A006512(j) + A006512(k) - 1, with n>3 and j<=k.
%e A205668 97 is here because neither 96 or 98 is the sum of two primes from the set {2, 3, 5, 7, 11, 13, 17, 19, 29, 31, 41, 43, 59, 61, 71, 73}, which are the twin primes less than 100. - _T. D. Noe_, Feb 12 2012
%t A205668 k=Insert[Select[Prime[Range[2,10^4]], PrimeQ[#-2]||PrimeQ[#+2]&], 5, 3]; u=Length@k/2; Complement[Prime[Range[4,10^4]], Select[Flatten[Join[Table[k[[2n-1]] + k[[2m-1]] + 1,{n,u}, {m,n}], Table[k[[2n]] + k[[2m]] - 1,{n,u}, {m,n}]]], PrimeQ]]
%o A205668 (PARI) lower=List();p=2;forprime(q=3,1e8,if(q-p==2,listput(lower,p));p=q)
%o A205668 isk(n)=for(i=1,#lower,if(setsearch(lower,n-lower[i]),return(lower[i]));if(2*lower[i]>n,return(0)));error("ran out")
%o A205668 is(n)=!isk(n-1)&&!isk(n-3) \\ _Charles R Greathouse IV_, Jan 31 2012
%Y A205668 Cf. A000040, A001359, A006512.
%K A205668 nonn
%O A205668 1,1
%A A205668 _Manuel Valdivia_, Jan 30 2012