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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. 1

%I

%S 2,7,106,193,241,286,322,353,411,415,753,858,859,1086,1164,1305,1547,

%T 1548,1625,1631,1648,1678,1896,1972,2007,2103,2406,2503,2515,2516,

%U 2530,2553,2638,2714,3003,3059,3060,3337,3903,4012,4072,4299,4386,4404,4625,4698

%N 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.

%t 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-Fran├žois Alcover at A002858 *)

%Y Cf. A002858, A068820, A307328.

%K nonn

%O 1,1

%A _Amiram Eldar_, Apr 02 2019

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Last modified January 18 01:05 EST 2020. Contains 330995 sequences. (Running on oeis4.)