

A084833


a(n) is the smallest number such that a(n) + a(n1), a(n) + a(n1) + a(n2), ..., a(n) + ... + a(1) are nonprime.


3



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
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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



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, b1, 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, pc1, s[i]=sum(k=i, pc1, p[k])); i=1; while (checkprime(x, pc), x++); p[pc]=x; pc++); p }


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



