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-4 is a square mod n.
6

%I #10 Mar 06 2020 15:49:22

%S 1,2,4,5,8,10,13,17,20,25,26,29,34,37,40,41,50,52,53,58,61,65,68,73,

%T 74,82,85,89,97,100,101,104,106,109,113,116,122,125,130,136,137,145,

%U 146,148,149,157,164,169,170,173,178,181,185,193,194,197,200,202,205,212

%N -4 is a square mod n.

%C Numbers that are not multiples of 16 and for which all odd prime factors are congruent to 1 mod 4. - _Eric M. Schmidt_, Apr 21 2013

%H Eric M. Schmidt, <a href="/A057129/b057129.txt">Table of n, a(n) for n = 1..1000</a>

%o (Sage)

%o def A057129(n) :

%o if n%16==0: return False

%o for (p, m) in factor(n) :

%o if p % 4 not in [1, 2] : return False

%o return True

%o # _Eric M. Schmidt_, Apr 21 2013

%Y Includes the primes in A002313 and these (primes congruent to {1, 2} mod 4) are the prime factors of the terms in this sequence. Cf. A008784, A057125, A057126, A057127, A057128.

%K nonn

%O 1,2

%A _Henry Bottomley_, Aug 10 2000