cp's OEIS Frontend

A084833 a(n) is the smallest number such that a(n) + a(n-1), a(n) + a(n-1) + a(n-2), ..., a(n) + ... + a(1) are nonprime.

%I A084833 #12 Jun 24 2023 07:55:50
%S A084833 1,3,5,1,15,9,15,6,3,6,21,6,3,6,15,6,3,6,3,9,3,9,15,6,3,6,3,9,9,9,3,9,
%T A084833 9,9,3,6,3,3,3,3,3,6,15,6,3,3,3,6,9,6,3,6,9,9,3,6,3,6,15,6,3,6,3,9,3,
%U A084833 9,3,9,9,6,3,6,9,6,3,3,3,6,3,9,3,6,3,3,3,6,3,6,3,6,9,6,3,3,3,6,9,6,3
%N A084833 a(n) is the smallest number such that a(n) + a(n-1), a(n) + a(n-1) + a(n-2), ..., a(n) + ... + a(1) are nonprime.
%C A084833 No sum of a continuous subsequence is ever prime. Does the sequence consist only of multiples of 3 after a(4)?
%e A084833 a(5) = 15 as 1+3+5+1+15 = 25 is composite, 3+5+1+15 = 24 is composite, 5+1+15 = 21 is composite, and 1+15 = 16 is composite, and no smaller number has this property.
%o A084833 (PARI) { checkprime(a,b)=local(fl); fl=0; for (i=1,b-1,if (isprime(a+s[i]),fl=1; break)); fl }
%o A084833 { p=vector(100); p[1]=1; pc=2; while (pc<100, x=1; s=vector(100); for (i=1,pc-1,s[i]=sum(k=i,pc-1,p[k])); i=1; while (checkprime(x,pc),x++); p[pc]=x; pc++); p }
%Y A084833 Cf. A084834.
%K A084833 nonn
%O A084833 1,2
%A A084833 _Jon Perry_, Jun 06 2003