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A068857
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a(0) = 0, a(1) = 8; for n>=2: a(n) = smallest multiple of a(n-1) which is of the form 2k*(2k+2).
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3
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0, 8, 24, 48, 288, 16128, 11950848, 4636929024, 88106288385024, 8038489644431643930624, 15177535939786079616000991061008232448, 40096515501441989312471498490435884509054125751527350190658560000
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OFFSET
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0,2
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LINKS
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FORMULA
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EXAMPLE
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24 = 4*6 is a member and the smallest multiple of 24 which is of the form 2k(2k+2) is 48 = 6*8.
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MATHEMATICA
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m = 0; {0} ~Join~ Rest@ NestList[(m++; While[! Divisible[Set[k, # (# + 2) &[2 m]], #], m++]; k) &, 1, 8] (* Michael De Vlieger, Mar 18 2024 *)
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PROG
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(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
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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