A076994 a(1) = 2, a(n+1) is the largest squarefree number < 2*a(n).

2, 3, 5, 7, 13, 23, 43, 85, 167, 331, 661, 1321, 2641, 5281, 10561, 21121, 42241, 84481, 168961, 337921, 675841, 1351681, 2703361, 5406721, 10813441, 21626881, 43253761, 86507521, 173015041, 346030081, 692060161, 1384120321, 2768240641

Offset: 1

Author

Amarnath Murthy, Oct 26 2002

Keywords

• nonn

Comments

Analogous to Bertrand's primes.

Links

• Hugo Pfoertner, Table of n, a(n) for n = 1..360

Crossrefs

Cf. A006992, A076995.

Programs

Maple

with(numtheory):a[1] := 2:for n from 2 to 84 do q := 2*a[n-1]-1:while(not issqrfree(q)) do q := q-1:od:a[n] := q:od:seq(a[l],l=1..84);

Mathematica

lsfn[n_]:=Module[{s=2n-1},While[!SquareFreeQ[s],s--];s]; NestList[ lsfn,2,40] (* Harvey P. Dale, Nov 28 2018 *)

Extensions

More terms from Sascha Kurz, Jan 26 2003