A240882 Numbers m such that m - 4*k^2 is a prime for all k > 0 with k^2 < m/4.
6, 7, 9, 11, 15, 21, 23, 27, 33, 35, 47, 77, 83, 143, 167, 227, 437
Offset: 1
Examples
21 is in this sequence because 21 - 4*1^2 = 17 and 21 - 4*2^2 = 5 are both prime.
Crossrefs
Cf. A240842.
Programs
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Mathematica
n=6;Monitor[Parallelize[While[True,If[MemberQ[PrimeQ[Table[n-4*k^2,{k,1,Floor[Sqrt[n/4]]}]],False]==False,Print[n]];n++];n],n] (* J.W.L. (Jan) Eerland, Mar 17 2024 *) -
PARI
isOK(n) = k=1; until(k^2>=n/4, if(!isprime(n-4*k^2), return(0)); k++); 1; for(n=3, 1000000, if(isOK(n), print1(n, ", "))) \\ Colin Barker, Apr 14 2014
Extensions
One missing term and one additional term from Colin Barker, Apr 14 2014
Comments