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Let M_k be the k X k matrix, M_(i,j) = 1 if i^2 + j^2 is squarefree, M_(i,j) = 0 otherwise; sequence gives values of k such that det(M_k) = 0.
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%I #18 Apr 06 2020 09:19:59

%S 6,7,8,9,10,12,13,14,15,16,20,23,27,29,30,31,32,34,35,36,37,38,39,46,

%T 47,48,49,50,57,58,59,65,66,67,68,69,70,71,95,96,97,98,99,100,101,102,

%U 103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123

%N Let M_k be the k X k matrix, M_(i,j) = 1 if i^2 + j^2 is squarefree, M_(i,j) = 0 otherwise; sequence gives values of k such that det(M_k) = 0.

%C No more terms <= 1100. - _David A. Corneth_, Apr 05 2020

%H Jinyuan Wang, <a href="/A069838/b069838.txt">Table of n, a(n) for n = 1..67</a>

%o (PARI) for(n=1,71,if(matdet(matrix(n,n,i,j,issquarefree(i^2+j^2)))==0,print1(n",")))

%Y Cf. A005117.

%K nonn

%O 1,1

%A _Benoit Cloitre_, Apr 21 2002

%E More terms from _Jinyuan Wang_, Apr 05 2020