|
|
A102415
|
|
Greatest semiprime less than n-th prime.
|
|
5
|
|
|
4, 6, 10, 10, 15, 15, 22, 26, 26, 35, 39, 39, 46, 51, 58, 58, 65, 69, 69, 77, 82, 87, 95, 95, 95, 106, 106, 111, 123, 129, 134, 134, 146, 146, 155, 161, 166, 169, 178, 178, 187, 187, 194, 194, 209, 221, 226, 226, 226, 237, 237, 249, 254, 262, 267, 267, 274, 278, 278
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
3,1
|
|
LINKS
|
Amiram Eldar, Table of n, a(n) for n = 3..10000
Eric Weisstein's World of Mathematics, Semiprime
|
|
FORMULA
|
a(n) < A000040(n) < A102414(n).
|
|
EXAMPLE
|
a(3) = 4 since 4 is the greatest semiprime less than prime(3) = 5.
|
|
MATHEMATICA
|
a[n_] := Module[{m = Prime[n] - 1}, While[PrimeOmega[m] != 2, m--]; m]; Array[a, 60, 3] (* Amiram Eldar, Feb 06 2020 *)
|
|
PROG
|
(PARI) a(n) = {sp = prime(n)-1; while(bigomega(sp) != 2, sp--); sp; } \\ Michel Marcus, Mar 04 2017
|
|
CROSSREFS
|
Cf. A001358, A102414, A102440.
Sequence in context: A193951 A129854 A088682 * A117003 A335032 A057670
Adjacent sequences: A102412 A102413 A102414 * A102416 A102417 A102418
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
Reinhard Zumkeller, Jan 08 2005
|
|
STATUS
|
approved
|
|
|
|