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A113880 Variation on Recamán's sequence utilizing the four basic operations (/ - + *) in that order. 0
1, 3, 6, 2, 7, 13, 20, 12, 21, 11, 22, 10, 23, 9, 24, 8, 25, 43, 62, 42, 63, 41, 18, 432, 407, 381, 354, 326, 297, 267, 236, 204, 171, 137, 102, 66, 29, 67, 28, 68, 27, 69, 26, 70, 115, 161, 114, 162, 113, 163, 112, 60, 3180, 3126, 3071, 3015, 2958, 51, 110, 50, 111, 49 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

More precisely:

a(n) = a(n-1)/n if a(n-1)/n is integer and not already in the sequence. Else:

a(n) = a(n-1)-n if a(n-1)-n is positive and not already in the sequence. Else:

a(n) = a(n-1)+n if a(n-1)+n is not already in the sequence. Else:

a(n) = a(n-1)*n if a(n-1)*n is not already in the sequence. Else STOP.

In other words, divide if you can, else subtract, else add, else multiply.

By a(1000) there are 3 division steps, 928 subtraction steps, 59 addition steps and 10 multiplication steps. It is unlikely that every number belongs to the sequence since there are many "holes". It is an open question if there are any repetitions after a multiplication step. Can anybody expand the series?

LINKS

Table of n, a(n) for n=1..62.

EXAMPLE

a(24)=432 because: a(23) = 18.

18/24 is not an integer.

18-24 is negative.

18 + 24 = 42 is already in the sequence

Therefore 18 * 24 = 432.

CROSSREFS

Cf. A005132.

Sequence in context: A064387 A064389 A118201 * A171884 A226940 A098141

Adjacent sequences:  A113877 A113878 A113879 * A113881 A113882 A113883

KEYWORD

nonn

AUTHOR

Sergio Pimentel, Jan 27 2006

STATUS

approved

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Last modified August 27 15:21 EDT 2014. Contains 246143 sequences.