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A320487 a(0) = 1; thereafter a(n) is obtained by applying the "delete multiple digits" map m -> A320485(m) to 2*a(n-1). 33
1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 3, 6, 12, 24, 48, 96, 192, 384, 768, 1536, 3072, 61, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 3, 6, 12, 24, 48, 96, 192, 384, 768, 1536, 3072, 61, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

In short, double the previous term and delete any digits appearing more than once.

Periodic with period 28.

Using the variant A320486 yields the same sequence, since the empty string never occurs. - M. F. Hasler, Oct 24 2018

Conjecture: If we start with any nonnegative integer and repeatedly double and apply the "delete multiple digits" map m -> A320485(m), we eventually reach 0 or 1 (see A323835). - N. J. A. Sloane, Feb 03 2019

REFERENCES

Eric Angelini, Posting to Sequence Fans Mailing List, Oct 24 2018

LINKS

Table of n, a(n) for n=0..56.

N. J. A. Sloane, Coordination Sequences, Planing Numbers, and Other Recent Sequences (II), Experimental Mathematics Seminar, Rutgers University, Jan 31 2019, Part I, Part 2, Slides. (Mentions this sequence)

EXAMPLE

2*32768 = 65536 -> 3 since we delete the multiple digits 6 and 5.

2*61 = 122 -> 1 since we delete the multiple 2's.

MATHEMATICA

a[1] = 1; a[n_] := a[n] = FromDigits[First /@ Select[ Tally[IntegerDigits[2 a[n - 1]]], #[[2]] == 1 &]] /* Stan Wagon, Nov 17 2018_ */

PROG

(PARI) A=[2]; for(i=1, 99, A=concat(A, A320486(A[#A]*2))); A \\ M. F. Hasler, Oct 24 2018

CROSSREFS

Cf. A000079, A065243, A320485, A323830.

See A035615 for a classic related base-2 sequence.

Sequence in context: A328679 A220051 A220493 * A323830 A118655 A249169

Adjacent sequences:  A320484 A320485 A320486 * A320488 A320489 A320490

KEYWORD

nonn,base

AUTHOR

N. J. A. Sloane, Oct 24 2018, following a suggestion from Eric Angelini.

STATUS

approved

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Last modified November 17 23:26 EST 2019. Contains 329242 sequences. (Running on oeis4.)