A073885 a(1)=1, a(n) = smallest positive integer not included earlier such that the n-th partial sum is a prime iff n is a prime.

1, 2, 4, 3, 7, 5, 9, 8, 6, 10, 12, 11, 19, 13, 14, 16, 17, 15, 21, 20, 18, 22, 24, 23, 25, 26, 27, 28, 33, 29, 31, 30, 32, 34, 35, 36, 43, 37, 38, 40, 39, 41, 49, 42, 45, 44, 67, 46, 47, 48, 50, 51, 54, 53, 52, 56, 57, 55, 63, 58, 60, 59, 61, 64, 62, 65, 69, 68, 66, 70, 72, 71

Offset

1,2

Links

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

Maple

S:= [$2..200]: # stop before the first term > 200
s:= 1: R:= 1:
for i from 2 do
  target:= isprime(i);
  found:= false;
  for j from 1 to nops(S) while not found do
    if isprime(s+S[j]) = target then
       found:= true;
       R:= R, S[j];
       s:= s+S[j];
       S:= subsop(j=NULL, S);
    fi
  od;
  if not found then break fi;
od:
R; # Robert Israel, Oct 07 2024

Mathematica

For[n=1; s={}; sum=0, n<=100, n++, For[v=1, MemberQ[s, v]||Xor[PrimeQ[n], PrimeQ[sum+v]], v++, Null]; sum+=v; AppendTo[s, a[n]=v]]; a/@Range[100]

Crossrefs

Cf. A073886.

Sequence in context: A120619 A346298 A084385 * A256283 A257465 A120234

Adjacent sequences: A073882 A073883 A073884 * A073886 A073887 A073888

Keyword

nonn

Author

Amarnath Murthy, Aug 17 2002

Extensions

Edited by Dean Hickerson, Oct 22 2002

Status

approved