cp's OEIS Frontend

A214879 Numbers that cannot be written as sum of the squares of two primes.

%I A214879 #16 Aug 13 2021 08:05:50
%S A214879 0,1,2,3,4,5,6,7,9,10,11,12,14,15,16,17,19,20,21,22,23,24,25,26,27,28,
%T A214879 30,31,32,33,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,51,52,54,55,
%U A214879 56,57,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,75,76
%N A214879 Numbers that cannot be written as sum of the squares of two primes.
%C A214879 A045698(a(n)) = 0.
%H A214879 Reinhard Zumkeller, <a href="/A214879/b214879.txt">Table of n, a(n) for n = 1..10000</a>
%F A214879 a(n) ~ n. - _Charles R Greathouse IV_, Sep 01 2015
%o A214879 (Haskell)
%o A214879 import Data.List (elemIndices)
%o A214879 a214879 n = a214879_list !! (n-1)
%o A214879 a214879_list = elemIndices 0 a045698_list
%o A214879 -- _Reinhard Zumkeller_, Jul 29 2012
%o A214879 (PARI) is(n)=forprime(p=2,sqrtint(n), if(isprimepower(n-p^2)==2, return(0))); 1 \\ _Charles R Greathouse IV_, Sep 01 2015
%o A214879 (Python)
%o A214879 from sympy import primerange
%o A214879 def aupto(limit):
%o A214879     primes = list(primerange(2, int((limit-4)**.5)+2))
%o A214879     nums = [p*p + q*q for i, p in enumerate(primes) for q in primes[i:]]
%o A214879     return sorted(set(range(limit+1)) - set(k for k in nums if k <= limit))
%o A214879 print(aupto(76)) # _Michael S. Branicky_, Aug 13 2021
%Y A214879 Cf. A045636 (complement).
%K A214879 nonn
%O A214879 1,3
%A A214879 _Reinhard Zumkeller_, Jul 29 2012