A048278 Positive numbers n such that the numbers binomial(n,k) are squarefree for all k = 0..n.

1, 2, 3, 5, 7, 11, 23

Offset

1,2

Comments

It has been shown by Granville and Ramaré that the sequence is complete.

These are all the positive integers m that, when m is represented in binary, contain no composites represented in binary as substrings. - Leroy Quet, Oct 30 2008

This is a number-theoretic sequence, so it automatically assumes that n is positive. To quote Granville and Ramaré, "From Theorem 2 it is evident that there are only finitely many rows of Pascal's Triangle in which all of the entries are squarefree. In section 2 we show that this only occurs in rows 1, 2, 3, 5, 7, 11 and 23 (a result proved by Erdős long ago)." - N. J. A. Sloane, Mar 06 2014

See also comment in A249441. - Vladimir Shevelev, Oct 29 2014

This sequence is equivalent to: Positive integers n such that Fibonacci(n+1) divides n!. This comment depends on the finiteness of A019532. - Altug Alkan, Mar 31 2016

Links

Table of n, a(n) for n=1..7.

A. Granville and O. Ramaré, Explicit bounds on exponential sums and the scarcity of squarefree binomial coefficients, Mathematika 43 (1996), 73-107, [DOI].

H. N. Ramaswamy and R. Siddaramu, On the Stufe, unit Stufe and Pythagoras number of the ring of integers modulo n, Adv. Stud. Contemp. Math. (Kyungshang) 20:3 (2010), pp. 373-388.

Formula

Integers n>0 in set difference between union (A000225, A055010) and A249452. - Vladimir Shevelev, Oct 30 2014

a(n) = A018253(n+1) - 1. - Altug Alkan, Apr 26 2016

Example

n=11: C[11,k] = 1, 11, 55, 165, 330, 462, ... are all squarefree (or 1).

Maple

select(n -> andmap(t -> numtheory:-issqrfree(binomial(n, t)), [$1..floor(n/2)]), [$1..100]); # Robert Israel, Oct 29 2014

Mathematica

Do[m = Prime[n]; k = 2; While[k < m/2 + .5 && Union[ Transpose[ FactorInteger[ Binomial[m, k]]] [[2]]] [[ -1]] < 2, k++ ]; If[k >= m/2 + .5, Print[ Prime[n]]], {n, 1, PrimePi[10^6]} ]
Select[Range[10^3], Function[n, AllTrue[Binomial[n, Range@ n], SquareFreeQ]]] (* Michael De Vlieger, Apr 01 2016, Version 10 *)

Prog

(PARI) is(n)=for(k=0, n\2, if(!issquarefree(binomial(n, k)), return(0))); 1 \\ Charles R Greathouse IV, Mar 06 2014

Crossrefs

Cf. A005117, A046098, A048276, A048277, A048279, A249441.

Cf. A000225, A055010, A249452.

Cf. A019532.

Sequence in context: A061165 A183055 A046689 * A247797 A068863 A284146

Adjacent sequences: A048275 A048276 A048277 * A048279 A048280 A048281

Keyword

nonn,fini,full

Author

Labos Elemer

Extensions

Edited by Ralf Stephan, Aug 03 2004

Status

approved