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A277558 A variation on Recamán's sequence (A005132): to get a(n), we first try to subtract n from a(n-1): a(n) = a(n-1)-n if positive and not already in the sequence; if not then a(n) = a(n-1)+n-i, where i >= 0 is the smallest number such that a(n-1)+n-i has not already appeared. 2
0, 1, 3, 6, 2, 7, 13, 20, 12, 21, 11, 22, 10, 23, 9, 24, 8, 25, 43, 62, 42, 63, 41, 18, 40, 15, 39, 66, 38, 67, 37, 68, 36, 69, 35, 70, 34, 71, 33, 72, 32, 73, 31, 74, 30, 75, 29, 76, 28, 77, 27, 78, 26, 79, 133, 188, 132, 189, 131, 190, 130, 191, 129, 192 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Is it ever impossible to extend the sequence -- meaning there is no number less than a(n-1)+n which has not appeared?

After 10^11 terms, the smallest number which has not appeared is 609790506.

LINKS

Benjamin Chaffin, Table of n, a(n) for n = 0..10000

EXAMPLE

a(23) = 18. To get a(24) we try 18-24, but that is negative; so we try 18+24 = 42, but 42 has already appeared; so we try 18+24-1, but 41 has also already appeared; so we try 18+24-2. 40 is positive and has not yet appeared, and so a(24) = 40.

CROSSREFS

Cf. A005132, A064387 (chooses a(n-1)+n+i instead of a(n-1)+n-i).

Sequence in context: A074170 A076543 A274648 * A005132 A064388 A064387

Adjacent sequences:  A277555 A277556 A277557 * A277559 A277560 A277561

KEYWORD

nonn

AUTHOR

Benjamin Chaffin, Oct 19 2016

STATUS

approved

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Last modified May 26 16:52 EDT 2017. Contains 287130 sequences.