A068007 Least number k such that the number of primes of the form [k/j] for j=1..k (A068050) is n, or zero if impossible.

1, 2, 5, 7, 10, 11, 15, 21, 0, 22, 23, 31, 34, 38, 35, 45, 50, 46, 47, 53, 62, 58, 59, 67, 69, 84, 70, 71, 79, 83, 87, 92, 93, 101, 94, 105, 95, 106, 107, 116, 117, 122, 118, 125, 119, 134, 135, 139, 146, 142, 149, 143, 156, 155, 158, 159, 171, 166, 167, 176, 175, 185

Offset

0,2

Comments

a(n) = 0 for n = 8, 94, 103, 122, 180, 283, 311, 353, 355, 398, ...

Links

Table of n, a(n) for n=0..61.

Mathematica

f[n_] := Count[ PrimeQ[ Floor[ n/Table[i, {i, Floor[n/2]} ]]], True]; a = Table[0, {100} ]; Do[b = f[n]; If[b < 100 && a[[b + 1]] == 0, a[[b + 1]] = n], {n, 1, 300}]; a

Crossrefs

Cf. A068050.

Sequence in context: A288602 A049842 A018636 * A224870 A033094 A206522

Adjacent sequences: A068004 A068005 A068006 * A068008 A068009 A068010

Keyword

nonn

Author

Robert G. Wilson v, Feb 12 2002

Extensions

Name corrected by Sean A. Irvine, Jan 18 2024

Status

approved