

A064387


Variation (2) on Recamán's sequence (A005132): to get a(n), we first try to subtract n from a(n1): a(n) = a(n1)n if positive and not already in the sequence; if not then a(n) = a(n1)+n+i, where i >= 0 is the smallest number such that a(n1)+n+i has not already appeared.


5



1, 3, 6, 2, 7, 13, 20, 12, 21, 11, 22, 10, 23, 9, 24, 8, 25, 43, 62, 42, 63, 41, 18, 44, 19, 45, 72, 100, 71, 101, 70, 38, 5, 39, 4, 40, 77, 115, 76, 36, 78, 120, 163, 119, 74, 28, 75, 27, 79, 29, 80, 132, 185, 131, 186, 130, 73, 15, 81, 141, 202
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OFFSET

1,2


COMMENTS

Variation (4) (A064389) is the nicest of these variations.
I would also like to get the following sequences: number of steps before n appears (or 0 if n never appears), list of numbers that never appear, height of n (cf. A064288, A064289, A064290), etc.


REFERENCES

Suggested by J. C. Lagarias.


LINKS

Table of n, a(n) for n=1..61.
Nick Hobson, Python program for this sequence
Index entries for sequences related to Recamán's sequence


MAPLE

h := array(1..100000); maxt := 100000; a := array(1..1000); a[1] := 1; h[1] := 1; for nx from 2 to 1000 do t1 := a[nx1]nx; if t1>0 and h[t1] <> 1 then a[nx] := t1; if t1 < maxt then h[t1] := 1; fi; else for i from 0 to 1000 do t1 := a[nx1]+nx+i; if h[t1] <> 1 then a[nx] := t1; if t1 < maxt then h[t1] := 1; fi; break; fi; od; fi; od; evalm(a);


CROSSREFS

Cf. A005132, A046901, A064388, A064389. Agrees with A064389 for first 187 terms, then diverges.
Sequence in context: A005132 A064388 * A064389 A118201 A274647 A113880
Adjacent sequences: A064384 A064385 A064386 * A064388 A064389 A064390


KEYWORD

nonn,easy


AUTHOR

N. J. A. Sloane, Sep 28 2001


STATUS

approved



