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Numbers n such that n^4+(n+1)^4 is not prime.
1

%I #14 Mar 31 2024 14:11:51

%S 5,7,10,11,15,17,18,19,20,21,22,23,24,28,29,30,32,35,39,41,42,44,45,

%T 46,47,49,50,51,52,53,55,56,57,58,59,60,61,62,64,65,66,69,70,71,73,75,

%U 76,77,79,80,81,83,84,85,86,90,91,92,93,94,95,96,99,100,101

%N Numbers n such that n^4+(n+1)^4 is not prime.

%H Vincenzo Librandi, <a href="/A241265/b241265.txt">Table of n, a(n) for n = 1..1000</a>

%F 7 is in this sequence because 7^4+8^4 = 6497 = 73*89.

%t Select[Range[200], ! PrimeQ[#^4 + (# + 1)^4] &]

%t Position[Total/@Partition[Range[120]^4,2,1],_?CompositeQ]//Flatten (* _Harvey P. Dale_, Mar 31 2024 *)

%o (Magma) [n: n in [1..200] | not IsPrime(n^4+(n+1)^4)];

%Y Complement of A155211.

%K nonn,easy

%O 1,1

%A _Vincenzo Librandi_, Apr 20 2014