A219786 Least number such that there are n-1 composite numbers between n+1 and a(n) (both inclusive).

4, 6, 9, 10, 14, 15, 18, 21, 24, 25, 27, 28, 32, 34, 36, 38, 40, 42, 45, 48, 50, 51, 54, 56, 58, 62, 64, 65, 68, 69, 72, 75, 77, 80, 82, 84, 86, 88, 91, 92, 94, 95, 98, 100, 104, 105, 108, 111, 114, 116, 118, 119, 121, 123, 125, 128, 130, 132, 134, 135

Offset

2,1

Comments

For n>1, a(n) is a lower bound for A219787(n). - Michel Marcus , Nov 28 2012.

Links

Table of n, a(n) for n=2..61.

P. Erdos and C. Pomerance, Matching the natural numbers up to n with distinct multiples in another interval, Nederl. Akad. Wetensch. Proc. Ser. A 83 (1980), 147-161.

Example

For n=4, a(n)=9 as there are 3 composite numbers between 5 and 9: 6, 8, and 9.
For n=11, a(n)= 25 with the 11 composite numbers: 12, 14, 15, 16, 18, 20, 21, 22, 24, 25 (cf comment in A219787).

Prog

(PARI) a(n) = {nbc = 0; nn = n+1; while (nbc != n-1, if (! isprime(nn), nbc++; ); if (nbc != n-1, nn++); ); return (nn); }

Crossrefs

Cf. A002808, A219787.

Sequence in context: A028260 A085155 A371555 * A302038 A063762 A320912

Adjacent sequences: A219783 A219784 A219785 * A219787 A219788 A219789

Keyword

nonn

Author

Michel Marcus, Nov 28 2012

Status

approved