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

1,1

Links

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

Formula

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

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 *)

Crossrefs

Cf. A002858, A068820.

Sequence in context: A084406 A075648 A071527 * A097095 A101755 A363847

Adjacent sequences: A307325 A307326 A307327 * A307329 A307330 A307331

Keyword

nonn,changed

Author

Amiram Eldar, Apr 02 2019

Status

approved