A171914 Van Eck sequence (cf. A181391) starting with a(1) = 4.

4, 0, 0, 1, 0, 2, 0, 2, 2, 1, 6, 0, 5, 0, 2, 6, 5, 4, 17, 0, 6, 5, 5, 1, 14, 0, 6, 6, 1, 5, 7, 0, 6, 5, 4, 17, 17, 1, 9, 0, 8, 0, 2, 28, 0, 3, 0, 2, 5, 15, 0, 4, 17, 16, 0, 4, 4, 1, 20, 0, 5, 12, 0, 3, 18, 0, 3, 3, 1, 11, 0, 5, 11, 3, 6, 42, 0, 6, 3, 5, 8, 40, 0, 6, 6, 1, 17, 34, 0, 6

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, i.e., a(n) does not appear earlier in the sequence. - M. F. Hasler, Jun 15 2019

Links

Table of n, a(n) for n=1..90.

Formula

a(n+1) = A181391(n) up to the first occurrence of a(1) = 4 in A181391. - M. F. Hasler, Jun 15 2019

Prog

(PARI) A171914_vec(N, a=4, 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 15 2019
(Python)
from itertools import count, islice
def A171914gen(): # generator of terms
    b, bdict = 4, {4:(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, )
A171914_list = list(islice(A171914gen(), 20)) # Chai Wah Wu, Dec 21 2021

Crossrefs

Cf. A181391, A171911, ..., A171918 (same but starting with 0, 1, ..., 8).

Sequence in context: A215061 A215060 A096623 * A200627 A152889 A216273

Adjacent sequences: A171911 A171912 A171913 * A171915 A171916 A171917

Keyword

nonn

Author

N. J. A. Sloane, Oct 22 2010

Extensions

Name edited and cross-references added by M. F. Hasler, Jun 15 2019

Status

approved