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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 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 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified May 24 16:32 EDT 2024. Contains 372781 sequences. (Running on oeis4.)