A214735 Primes such that no pairwise sum is a square.
2, 3, 5, 17, 29, 37, 41, 43, 53, 67, 73, 89, 109, 113, 131, 137, 149, 151, 157, 163, 181, 197, 199, 229, 233, 241, 277, 293, 313, 317, 331, 337, 349, 367, 373, 389, 401, 409, 421, 433, 449, 457, 461, 521, 541, 557, 577, 593, 601, 613, 617, 619, 631, 641, 643
Offset: 1
Keywords
Examples
a(3) = 5 because 2 + 5 = 7 (not a square) and 3 + 5 = 8 (a cube, not a square). 7 is not in the sequence because 2 + 7 = 3^2. With 11, we have 11 + 5 = 4^2, and for 13, there is 3 + 13 = 4^2. a(4) = 17, as 2 + 17 = 19 (a prime), 3 + 17 = 20 (divisible by a square but not itself a square) and 5 + 17 = 22 (a squarefree semiprime).
Links
- Zak Seidov, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
t = {2}; currPrime = 2; len = 1; maxLen = 100; Do[Label[ne]; currPrime = NextPrime[currPrime]; Do[If[IntegerQ[Sqrt[t[[i]] + currPrime]], Goto[ne]], {i, len}]; AppendTo[t, currPrime]; len++, {maxLen - 1}]; t -
PARI
list(lim)=my(v=List([2])); forprime(p=3,lim, if(issquare(p+2), next); for(k=sqrtint(p+2)+1,sqrtint(2*p-2), if(setsearch(v,k^2-p), next(2))); listput(v, p)); Vec(v) \\ Charles R Greathouse IV, Feb 14 2017
Comments