OFFSET
0,2
LINKS
Chai Wah Wu, Table of n, a(n) for n = 0..14
FORMULA
a(n) = 8 * A068776(n-1) for n>=1.
EXAMPLE
24 = 4*6 is a member and the smallest multiple of 24 which is of the form 2k(2k+2) is 48 = 6*8.
MATHEMATICA
m = 0; {0} ~Join~ Rest@ NestList[(m++; While[! Divisible[Set[k, # (# + 2) &[2 m]], #], m++]; k) &, 1, 8] (* Michael De Vlieger, Mar 18 2024 *)
PROG
(Python)
from itertools import islice
from sympy import sqrt_mod_iter
def A068857_gen(): # generator of terms
yield 0
a = 8
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&1 and d < b:
b = d
a = b**2-1
CROSSREFS
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Mar 12 2002
EXTENSIONS
More terms from Sascha Kurz, Mar 23 2002
a(8) onward corrected by Sean A. Irvine, Mar 18 2024
a(10)-a(11) from Alois P. Heinz, Mar 19 2024
STATUS
approved