A111238 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

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 A387570 A089421

Adjacent sequences: A111235 A111236 A111237 * A111239 A111240 A111241

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Oct 30 2005

STATUS

approved