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Indices of prime Ulam numbers: numbers k such that A002858(k) is prime.
3

%I #17 May 13 2024 05:21:16

%S 2,3,7,8,15,17,25,31,41,48,69,73,91,97,106,107,123,125,138,167,172,

%T 177,181,193,194,241,242,246,267,280,286,287,297,306,312,322,323,338,

%U 340,343,353,354,382,388,393,398,403,411,412,415,416,433,444,448,460

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

%H Amiram Eldar, <a href="/A307328/b307328.txt">Table of n, a(n) for n = 1..10000</a>

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

%t 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 *)

%Y Cf. A002858, A068820.

%K nonn

%O 1,1

%A _Amiram Eldar_, Apr 02 2019