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.

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, 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, 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

Offset

1,2

Comments

No sum of a continuous subsequence is ever prime. Does the sequence consist only of multiples of 3 after a(4)?

Links

Table of n, a(n) for n=1..99.

Example

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.

Prog

(PARI) { checkprime(a, b)=local(fl); fl=0; for (i=1, b-1, if (isprime(a+s[i]), fl=1; break)); fl }
{ 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 }

Crossrefs

Cf. A084834.

Sequence in context: A143250 A221494 A174883 * A204020 A265649 A216520

Adjacent sequences: A084830 A084831 A084832 * A084834 A084835 A084836

Keyword

nonn

Author

Jon Perry, Jun 06 2003

Status

approved