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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 not prime. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

No sum of a continuous subsequence is ever prime. The sequence consists only of multiples of 3 after n=4?

LINKS

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

EXAMPLE

a(5)=15 as 1+3+5+1+15=25, 3+5+1+15=24 and 5+1+15=21

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

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Last modified September 18 23:30 EDT 2020. Contains 337175 sequences. (Running on oeis4.)