login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A285767 Cyclops octagonal numbers: a(n) = n*(3*n-2) with one “zero” digit in the middle. 0
0, 408, 11041, 18096, 22016, 23056, 28033, 38081, 56033, 61061, 1140833, 1170625, 1250656, 1410416, 1460216, 1540833, 2120161, 2130261, 2140385, 2150533, 2310896, 2390561, 2460696, 2520833, 2570576, 2780181, 2920533, 3230256, 3280256, 3490565, 3660865, 3680776 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The n-th octagonal number x(n) = n*(3*n - 2).

Subset of A000567.

All the terms have the number of digits odd with only one “zero” digit in the middle.

LINKS

Table of n, a(n) for n=1..32.

EXAMPLE

For n = 12; x(12) = 12*(3*12 - 2) = 408 that is 12th octagonal number with one zero digit in the middle, hence appears in the sequence.

For n = 61; x(61) = 61*(3*61 - 2) = 11041 that is 61st octagonal number with one zero digit in the middle, hence appears in the sequence.

MAPLE

iscyclops:= proc(n) local L, t;

t:= ilog10(n);

if t::odd then return false fi;

L:= convert(n, base, 10);

L[1+t/2] = 0 and numboccur(0, L) = 1

end proc:

iscyclops(0):= true:

select(iscyclops, [seq(n*(3*n-2), n=0..1000)]);

MATHEMATICA

Select[Table[n (3 n - 2), {n, 0, 1110}], And[OddQ@ Length@ #, Count[#, 0] == 1, Take[#, {Ceiling[Length[#]/2]}] == {0}] &@ IntegerDigits@ # &] (* Michael De Vlieger, Apr 26 2017 *)

CROSSREFS

Intersection of A000567 and A134808.

Cf. A000567, A134808, A134809, A160717.

Sequence in context: A234697 A337795 A183717 * A282479 A163024 A283948

Adjacent sequences:  A285764 A285765 A285766 * A285768 A285769 A285770

KEYWORD

nonn,base

AUTHOR

K. D. Bajpai, Apr 25 2017

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 7 12:30 EDT 2022. Contains 355986 sequences. (Running on oeis4.)