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A171899 Backwards Van Eck transform of A000002. 3
0, 0, 1, 3, 1, 3, 2, 2, 1, 3, 2, 1, 3, 1, 3, 2, 1, 3, 1, 3, 2, 2, 1, 3, 2, 2, 1, 3, 1, 3, 2, 1, 3, 2, 2, 1, 3, 2, 1, 3, 1, 3, 2, 2, 1, 3, 2, 2, 1, 3, 2, 1, 3, 1, 3, 2, 1, 3, 1, 3, 2, 2, 1, 3, 2, 1, 3, 1, 3, 2, 1, 3, 2, 2, 1, 3, 2, 2, 1, 3, 1, 3, 2, 1, 3, 1, 3, 2, 2, 1, 3, 2, 1, 3, 1, 3, 2, 1, 3, 1, 3, 2, 2, 1, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

Given a sequence a, the backwards Van Eck transform b is defined as follows: If a[n] has already appeared in a, let a[m] be the most recent occurrence, and set b[n]=n-m; otherwise b[n]=0.

The forwards Van Eck transform of A000002 is A078929.

LINKS

Table of n, a(n) for n=1..105.

MAPLE

ECKb:=proc(a) local b, i, m, n;

if whattype(a) <> list then RETURN([]); fi:

b:=[0];

for n from 2 to nops(a) do

# has a(n) appeared before?

m:=0;

for i from n-1 by -1 to 1 do

if (a[i]=a[n]) then m:=n-i; break; fi

od:

b:=[op(b), m];

od:

RETURN(b);

end:

CROSSREFS

Cf. A000002, A181391, A171898, A078929.

Sequence in context: A271617 A057741 A133571 * A213885 A083208 A126682

Adjacent sequences:  A171896 A171897 A171898 * A171900 A171901 A171902

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Oct 22 2010

STATUS

approved

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Last modified April 24 07:25 EDT 2017. Contains 285338 sequences.