A111238 Indices k where A109890(k) is prime.

2, 3, 9, 22, 23, 24, 31, 39, 40, 43, 44, 47, 48, 49, 50, 58, 59, 66, 67, 70, 76, 81, 84, 88, 89, 97, 98, 100, 119, 122, 123, 130, 131, 138, 139, 144, 145, 150, 151, 152, 163, 168, 174, 178, 179, 185, 197, 200, 204, 207, 217, 218, 221, 225, 226, 227

Offset

1,1

Links

Michael De Vlieger, Table of n, a(n) for n = 1..10000

Michael De Vlieger, Log log scatterplot of A109890(n), n = 1..10^5, showing primes in red and nonprimes in dark blue.

Mathematica

nn = 240; c[_] := False; a[1] = 1; a[2] = 2; s = 3; c[1] = c[2] = True;
{2}~Join~Reap[Monitor[Do[k = SelectFirst[Divisors[s], ! c[#] &];
  c[k] = True; s += k;
If[PrimeQ[k], Sow[n]], {n, 3, nn}], n] ][[-1, 1]] (* Michael De Vlieger, Apr 27 2024 *)

Crossrefs

Cf. A109890, A111238, A111239, A111240.

Sequence in context: A324614 A141505 A111360 * A057832 A089421 A151825

Adjacent sequences: A111235 A111236 A111237 * A111239 A111240 A111241

Keyword

nonn

Author

N. J. A. Sloane, Oct 30 2005

Status

approved