A188347 Central element of a series of 7 successive nonsquarefree numbers.

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

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