A113425 Smallest prime closest to n^2.

2, 3, 7, 17, 23, 37, 47, 61, 79, 101, 127, 139, 167, 197, 223, 257, 293, 317, 359, 401, 439, 487, 523, 577, 619, 677, 727, 787, 839, 907, 967, 1021, 1087, 1153, 1223, 1297, 1367, 1447, 1523, 1601, 1669, 1759, 1847, 1933, 2027, 2113, 2207, 2309, 2399, 2503

Offset: 1

Author

Reinhard Zumkeller, Oct 31 2005

Keywords

• nonn

Comments

A060272(n) = abs(A000290(n) - a(n));

a(n) <= A113426(n).

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Programs

Maple

f:= proc(n) local k,d;
  for k from 1 do
    for d in [-1,1] do
      if isprime(n^2 + k*d) then return n^2 + k*d fi
  od od
end proc:
map(f, [$1..100]); # Robert Israel, Mar 10 2017

Mathematica

sp[n_]:=Module[{n2=n^2 ,npu,npd},npu=NextPrime[n2]; npd=NextPrime[n2,-1]; If[n2-npd<=npu-n2,npd,npu]]; sp/@Range[50]  (* Harvey P. Dale, Feb 05 2011 *)