A307329 Indices of twin Ulam primes: numbers k such that both u(k) and u(k+1) are primes, where u(k) = A002858(k) are the Ulam numbers.

2, 7, 106, 193, 241, 286, 322, 353, 411, 415, 753, 858, 859, 1086, 1164, 1305, 1547, 1548, 1625, 1631, 1648, 1678, 1896, 1972, 2007, 2103, 2406, 2503, 2515, 2516, 2530, 2553, 2638, 2714, 3003, 3059, 3060, 3337, 3903, 4012, 4072, 4299, 4386, 4404, 4625, 4698

Offset

1,1

Links

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

Mathematica

ulams = {1, 2}; Do[AppendTo[ulams, n = Last[ulams]; While[n++; Length[ DeleteCases[Intersection[ulams, n - ulams], n/2, 1, 1]] != 2]; n], {1000}]; p=PrimeQ[ulams]; len=Length[p]; s={}; Do[If[p[[n]]&&p[[n+1]], AppendTo[s, n]], {n, 1, len-1}]; s (* after Jean-François Alcover at A002858 *)

Crossrefs

Cf. A002858, A068820, A307328.

Sequence in context: A102747 A122524 A229165 * A162634 A235470 A072664

Adjacent sequences: A307326 A307327 A307328 * A307330 A307331 A307332

Keyword

nonn

Author

Amiram Eldar, Apr 02 2019

Status

approved