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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. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
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
Sequence in context: A102747 A122524 A229165 * A162634 A235470 A072664
KEYWORD
nonn
AUTHOR
Amiram Eldar, Apr 02 2019
STATUS
approved

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Last modified April 23 06:04 EDT 2024. Contains 371906 sequences. (Running on oeis4.)