A307328 Indices of prime Ulam numbers: numbers k such that A002858(k) is prime.

2, 3, 7, 8, 15, 17, 25, 31, 41, 48, 69, 73, 91, 97, 106, 107, 123, 125, 138, 167, 172, 177, 181, 193, 194, 241, 242, 246, 267, 280, 286, 287, 297, 306, 312, 322, 323, 338, 340, 343, 353, 354, 382, 388, 393, 398, 403, 411, 412, 415, 416, 433, 444, 448, 460

Offset: 1

Author

Amiram Eldar, Apr 02 2019

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A002858, A068820.

Programs

Mathematica

ulams = {1, 2}; Do[AppendTo[ulams, n = Last[ulams]; While[n++; Length[ DeleteCases[Intersection[ulams, n - ulams], n/2, 1, 1]] != 2]; n], {100}]; Flatten[Position[ulams, ?(PrimeQ[#] &)]] (* after _Jean-François Alcover at A002858 *)

Formula

A002858(a(n)) = A068820(n).