|
|
A068859
|
|
a(1) = 3 = 1*3; a(n) = smallest multiple of a(n-1) which is of the form k(k+2).
|
|
2
|
|
|
3, 15, 120, 360, 5040, 201600, 256032000, 4064251968000, 1024126980000259968000, 29365589556381243259975904529351552000, 82421263677202543043706796882184010324019881962069201381742720000
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
EXAMPLE
|
120 = 10*12 belongs to this sequence and 360 = 18*20 is the smallest such multiple of 120.
|
|
PROG
|
(Python)
from itertools import islice
from sympy import sqrt_mod_iter
def A068859_gen(): # generator of terms
a = 3
while True:
yield a
b = a+1
for d in sqrt_mod_iter(1, a):
if d==1 or d**2-1 == a:
d += a
if d < b:
b = d
a = b**2-1
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|