A047210 - OEIS

%I #17 Jun 18 2022 14:16:40

%S 0,1,1,1,4,4,4,4,7,9,9,9,12,11,10,9,16,16,17,16,18,20,18,16,24,25,25,

%T 25,28,25,28,25,31,33,30,28,36,36,36,36,40,39,41,37,40,41,42,36,46,49,

%U 49,49,52,52,49,49,55,57,57,49,60,59,58,57,64,64,65,64,64,65,64,64,72

%N Largest square modulo n.

%H T. D. Noe, <a href="/A047210/b047210.txt">Table of n, a(n) for n=1..1000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/QuadraticResidue.html">Quadratic Residue</a>

%t Table[r=Range[n]; Max[Mod[r^2, n]], {n, 100}] (* _T. D. Noe_, Dec 18 2008 *)

%t Table[r = Range[1 + n/2]; Max[Mod[r^2, n]], {n, 100}] (* _Zak Seidov_, Dec 18 2008 *)

%o Contribution from _Michael B. Porter_, May 04 2010: (Start)

%o (PARI) residue(n,m)={local(r);r=0;for(i=0,floor(m/2),if(i^2%m==n,r=1));r}

%o A047210(n)={local(r,m);r=0;m=n;while(r==0,m=m-1;if(residue(m,n),r=1));m} (End)

%Y Last elements of rows of A096008.

%K easy,nonn

%O 1,5

%A _Henry Bottomley_, Jun 08 2000