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A066805
a(n) is the least k such that n + Sum_{i=1..k} A018252(i) is prime; or 0 if none exists.
0
1, 1, 5, 1, 6, 1, 8, 2, 5, 1, 7, 1, 5, 2, 5, 1, 7, 1, 5, 3, 6, 1, 6, 2, 5, 2, 13, 1, 6, 1, 5, 2, 5, 4, 6, 1, 8, 2, 5, 1, 6, 1, 5, 10, 5, 1, 7, 2, 8, 3, 5, 1, 7, 2, 5, 2, 7, 1, 6, 1, 5, 2, 6, 4, 6, 1, 8, 2, 5, 1, 6, 1, 5, 2, 5, 27, 7, 1, 5, 11, 5, 1, 15, 2, 5
OFFSET
1,3
COMMENTS
Is a(n) nonzero for all n? If so, then every n can be represented as the difference of a prime and a partial sum of the nonprime numbers series. See A066753 for a related possible representation of n as the difference of a prime and a partial sum of the prime numbers series.
EXAMPLE
3 + (1 + 4 + 6 + 8 + 9) = 31, a prime and 5 consecutive nonprime numbers starting with 1 are required to achieve this. Hence a(3) = 5.
PROG
(PARI) a(n) = my(c=0, s=n); for(k=1, oo, until(!isprime(c), c++); if(isprime(s+=c), return(k))); \\ Jinyuan Wang, Jul 30 2020
CROSSREFS
Sequence in context: A190185 A331189 A176123 * A326142 A028284 A359169
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Jan 19 2002
EXTENSIONS
More terms from Larry Reeves (larryr(AT)acm.org), Jun 12 2002
STATUS
approved