login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A333211 Variation of Van Eck's sequence A181391: a(n+1) = the minimum positive offset m from a(n) such that a(n-m-1)*a(n-m) = a(n-1)*a(n); a(n+1)=0 if no such m exists. Start with a(1) = a(2) = 0. 2
0, 0, 0, 1, 1, 0, 2, 1, 0, 2, 1, 3, 0, 3, 1, 3, 1, 1, 13, 0, 6, 1, 0, 2, 1, 14, 0, 3, 1, 12, 0, 3, 1, 4, 0, 3, 1, 4, 4, 0, 4, 1, 4, 1, 1, 27, 0, 6, 1, 27, 4, 0, 4, 1, 10, 0, 3, 1, 21, 0, 3, 1, 4, 9, 0, 4, 1, 4, 1, 1, 25, 0, 6, 1, 25, 4, 0, 4, 1, 10, 25 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,7

COMMENTS

After 100 million terms the smallest number not appearing is 179549, while the smallest product of adjacent terms not appearing is 2969.

LINKS

Scott R. Shannon, Table of n, a(n) for n = 1..10000.

Brady Haran and N. J. A. Sloane, Don't Know (the Van Eck Sequence), Numberphile video (2019).

EXAMPLE

a(3) = 0 as a(1)*a(2) = 0*0 = 0, which has not previously appeared as the product of two adjacent terms.

a(4) = 1 as a(2)*a(3) = 0*0 = 0, which equals the product a(1)*a(2), one term back from a(3).

a(5) = 1 as a(3)*a(4) = 0*1 = 0, which equals the product a(2)*a(3), one term back from a(3).

a(6) = 0 as a(4)*a(5) = 1*1 = 1, which has not previously appeared as the product of two adjacent terms.

a(19) = 13 as a(17)*a(18) = 1*1 = 1, which equals the product a(4)*a(5), thirteen terms back from a(18).

CROSSREFS

Cf. A181391, A171898, A308721, A333210.

Sequence in context: A215345 A022329 A087466 * A258033 A153248 A221179

Adjacent sequences:  A333208 A333209 A333210 * A333212 A333213 A333214

KEYWORD

nonn

AUTHOR

Scott R. Shannon, Mar 11 2020

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 8 07:16 EDT 2020. Contains 335513 sequences. (Running on oeis4.)