|
| |
|
|
A107890
|
|
Semiprimes that are the product of two members of A007645.
|
|
2
|
|
|
|
9, 21, 39, 49, 57, 91, 93, 111, 129, 133, 169, 183, 201, 217, 219, 237, 247, 259, 291, 301, 309, 327, 361, 381, 403, 417, 427, 453, 469, 471, 481, 489, 511, 543, 553, 559, 579, 589, 597, 633, 669, 679, 687, 703, 721, 723, 763, 793, 813, 817, 831, 849, 871
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,1
|
|
|
REFERENCES
|
Conway, J. H. and Guy, R. K., The Book of Numbers. New York: Springer-Verlag, pp. 220-223, 1996.
Wagon, S. "Eisenstein Primes." Section 9.8 in Mathematica in Action. New York: W. H. Freeman, pp. 319-323, 1991.
|
|
|
LINKS
|
Robert Israel, Table of n, a(n) for n = 1..10000
Eric Weisstein's World of Mathematics, Eisenstein Integer.
Eric Weisstein's World of Mathematics, Eisenstein Prime.
Eric Weisstein's World of Mathematics, Semiprime.
|
|
|
FORMULA
|
{a(n)} = {p*q: p and q both elements of A007645} = {p*q: p and q both of form 3*m^2 * n^2 for integers m, n}.
|
|
|
MAPLE
|
N:= 1000: # for terms <= N
P:= [3, op(select(isprime, [seq(i, i=1..N/3, 6)]))]:
R:= NULL:
for i from 1 while P[i]^2 <= N do
m:= ListTools:-BinaryPlace(P, N/P[i]+1/2);
R:= R, seq(P[i]*P[j], j=i..m);
od:
sort([R]); # Robert Israel, Aug 28 2020
|
|
|
CROSSREFS
|
Cf. A001358, A007645, A108164.
Sequence in context: A059993 A036704 A338911 * A110209 A184040 A242990
Adjacent sequences: A107887 A107888 A107889 * A107891 A107892 A107893
|
|
|
KEYWORD
|
easy,nonn
|
|
|
AUTHOR
|
Jonathan Vos Post, Jun 12 2005
|
|
|
EXTENSIONS
|
Edited by Ray Chandler, Oct 15 2005
Definition corrected by N. J. A. Sloane, Feb 06 2008
|
|
|
STATUS
|
approved
|
| |
|
|
