A081258 Numbers k > 1 such that k^3 - 1 (or equivalently k^2 + k + 1) has no prime factor greater than k.

16, 18, 22, 30, 49, 67, 68, 74, 79, 81, 87, 100, 102, 121, 135, 137, 146, 149, 154, 158, 159, 163, 165, 169, 172, 178, 181, 191, 211, 221, 229, 230, 235, 256, 262, 263, 269, 273, 277, 291, 292, 301, 305, 313, 315, 324, 326, 334, 352, 361, 372, 373, 380, 393

Offset

1,1

Comments

One might also include 1 as a term here. - R. J. Mathar, Oct 11 2011

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

16 is a term: 16^3 - 1 = 4095 = 3*3*5*7*13.

Maple

isA081258 := proc(n)
        numtheory[factorset](n^3-1) ;
        if max(op(%)) <= n then
                true;
        else
                false;
        end if;
end proc;
for n from 1 to 400 do
        if isA081258(n) then
                printf("%d, ", n);
        end if;
end do: # R. J. Mathar, Oct 11 2011

Mathematica

Select[Range[2, 1000], FactorInteger[#^3 - 1][[-1, 1]] <= #&] (* Jean-François Alcover, Jun 15 2020 *)

Crossrefs

Cf. A081256, A081257.

Sequence in context: A065426 A308607 A097746 * A317423 A337374 A255847

Adjacent sequences: A081255 A081256 A081257 * A081259 A081260 A081261

Keyword

easy,nonn

Author

Jan Fricke, Mar 14 2003

Extensions

Name changed by Robert Israel, Nov 11 2016

Status

approved