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!)
A188347 Central element of a series of 7 successive nonsquarefree numbers. 2
217073, 671349, 826827, 1092750, 1092751, 1427373, 2097051, 2779373, 3112822, 3306447, 3597726, 3994823, 4063777, 4442877, 4630547, 4842477, 5436378, 5479622, 5610647, 5634125, 6315022, 6474223, 6626322, 6677867, 7128474, 7216621, 7216622, 7295451, 7507926 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Each of a(n), a(n)-1, a(n)-2, a(n)-3, a(n)+1, a(n)+2, a(n)+3 has at least one square divisor.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A077640(n) + 3. - Amiram Eldar, Feb 09 2021

EXAMPLE

217073=17*113^2, 217073-1=2^4*13567, 217073-2=3^2*89*271, 217073-3=2*5*7^2*443, 217073+1=2*3*11^2*13*23, 217073+2=5^2*19*457, 217073+3=2^2*54269.

MATHEMATICA

Select[Range[200000, 5000000], !SquareFreeQ[#] &&!SquareFreeQ[#-1] &&!SquareFreeQ[#+1] &&!SquareFreeQ[#-2] &&!SquareFreeQ[#+2] &&!SquareFreeQ[#-3] &&!SquareFreeQ[#+3]&]

CROSSREFS

Cf. A005117, A013929, A077640, A188296.

Sequence in context: A251804 A184668 A077640 * A078520 A019291 A205734

Adjacent sequences:  A188344 A188345 A188346 * A188348 A188349 A188350

KEYWORD

nonn

AUTHOR

Vladimir Joseph Stephan Orlovsky, Mar 29 2011

EXTENSIONS

More terms from Carl Najafi, Aug 22 2011

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 May 18 16:07 EDT 2021. Contains 343995 sequences. (Running on oeis4.)