OFFSET
1,1
COMMENTS
A van Eck sequence is defined recursively by a(n+1) = min { k > 0 | a(n-k) = a(n) } or 0 if this set is empty. - M. F. Hasler, Jun 12 2019
MATHEMATICA
t = {2};
Do[
d = Quiet[Check[Position[t, Last[t]][[-2]][[1]], 0]];
If[d == 0, x = 0, x = Length[t] - d];
AppendTo[t, x], 100]
t (* Horst H. Manninger, Aug 30 2020 *)
PROG
(PARI) A171912_vec(N, a=2, i=Map())={vector(N, n, a=if(n>1, iferr(n-mapget(i, a), E, 0)+mapput(i, a, n), a))} \\ M. F. Hasler, Jun 11 2019
(Python)
from itertools import count, islice
def A171912gen(): # generator of terms
b, bdict = 2, {2:(1, )}
for n in count(2):
yield b
if len(l := bdict[b]) > 1:
b = n-1-l[-2]
else:
b = 0
if b in bdict:
bdict[b] = (bdict[b][-1], n)
else:
bdict[b] = (n, )
A171912_list = list(islice(A171912gen(), 20)) # Chai Wah Wu, Dec 21 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Oct 22 2010
EXTENSIONS
Name edited and cross-references added by M. F. Hasler, Jun 12 2019
STATUS
approved