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 A174051 Composite numbers of the form x^2+y^2, gcd(x,y) = 1 1

%I

%S 10,25,26,34,50,58,65,74,82,85,106,122,125,130,145,146,169,170,178,

%T 185,194,202,205,218,221,226,250,265,274,289,290,298,305,314,325,338,

%U 346,362,365,370,377,386,394,410,425,442,445,458,466,481,482,485,493,505

%N Composite numbers of the form x^2+y^2, gcd(x,y) = 1

%C Composite numbers in A008784. - _R. J. Mathar_, Jul 08 2012

%H Charles R Greathouse IV, <a href="/A174051/b174051.txt">Table of n, a(n) for n = 1..10000</a>

%e 10 is in the sequence because 10 = 1^2 + 3^2 = 2*5;

%e 25 is in the sequence because 25 = 3^2 + 4^2 = 5*5;

%e 65 is in the sequence because 65 = 1 + 8^2 = 4^2 + 7^2 = 5*13.

%p with(numtheory):T:=array(0..50000000):U=array(0..50000000 ):k:=1:for x from 1 to 1000 do:for y from x to 1000 do:if type(x^2+y^2,prime)=false and gcd(x,y)=1 then T[k]:=x^2+y^2:k:=k+1:else fi: od :od:mini:=T[1]:ii:=1:for p from 1 to k-1 do:or n from 1 to k-1 do:if T[n] < mini then mini:= T[n]:ii:=n: indice:=U[n]: else fi:od:print(mini):T[ii]:= 99999999: ii:=1:mini:=T[1] :od:

%o (PARI) list(lim)=my(v=List(), x2, t); lim\=1; for(x=3, sqrtint(lim-1), x2=x^2; for(y=1, min(x-1, sqrtint(lim-x2)), if(gcd(x, y)==1 && !isprime(t=x2+y^2), listput(v, t)))); Set(v) \\ _Charles R Greathouse IV_, Jan 27 2018

%Y Cf. A002808, A002313, A037942.

%K nonn

%O 1,1

%A _Michel Lagneau_, Mar 06 2010

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Last modified June 4 17:50 EDT 2020. Contains 334828 sequences. (Running on oeis4.)