cp's OEIS Frontend

A119751 a(1) = 1; a(n) = first odd number greater than a(n-1) such that a(n) + a(i) + 1 is prime for all i=1,2,...,n.

%I A119751 #20 Mar 07 2023 03:06:50
%S A119751 1,3,9,69,429,4089,86529,513099,913569,7914339,6593621379,9366241599,
%T A119751 456246278469,4565283812559
%N A119751 a(1) = 1; a(n) = first odd number greater than a(n-1) such that a(n) + a(i) + 1 is prime for all i=1,2,...,n.
%F A119751 2*a(n)+1 = A113875(n). - _Don Reble_, Aug 17 2021
%t A119751 Table[If[n == 1, a[1] = 1, j = a[n - 1] + 2; While[a[n] = j; !
%t A119751     AllTrue[Table[a[i] + a[n] + 1, {i, 1, n}], PrimeQ], j += 2]; j]
%t A119751 , {n, 1, 7}] (* _Robert Price_, Apr 03 2019 *)
%o A119751 (PARI) isok(va, k, n) = if (isprime(2*k+1), for (i=1, n-1, if (! isprime(va[i]+k+1), return(0))); return(1));
%o A119751 lista(nn) = my(va=vector(nn)); va[1]=1; for (n=2, nn, my(k=va[n-1]+2); while (!isok(va, k, n), k+=2); va[n] = k); va; \\ _Michel Marcus_, Mar 07 2023
%Y A119751 Cf. A113875, A119752.
%K A119751 nonn,hard,more
%O A119751 1,2
%A A119751 _Walter Kehowski_, Jun 17 2006
%E A119751 a(13)-a(14) from _Donovan Johnson_, Mar 23 2008
%E A119751 Corrected and edited by _Walter Kehowski_, Oct 18 2008