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

Author

Vladimir Joseph Stephan Orlovsky, Mar 29 2011

Keywords

• nonn

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.

Examples

			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.
		

Links

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

Crossrefs

Cf. A005117, A013929, A077640, A188296.

Programs

Mathematica

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

Formula

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

Extensions

More terms from Carl Najafi, Aug 22 2011