login
A219786
Least number such that there are n-1 composite numbers between n+1 and a(n) (both inclusive).
1
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
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
Sequence in context: A028260 A085155 A371555 * A302038 A063762 A320912
KEYWORD
nonn
AUTHOR
Michel Marcus, Nov 28 2012
STATUS
approved