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a(n) = prime(2^n)-1.
4

%I #10 Sep 04 2022 13:15:13

%S 1,2,6,18,52,130,310,718,1618,3670,8160,17862,38872,84016,180502,

%T 386092,821640,1742536,3681130,7754076,16290046,34136028,71378568,

%U 148948138,310248240,645155196,1339484196,2777105128,5750079046

%N a(n) = prime(2^n)-1.

%H Paul Cooijmans, <a href="http://web.archive.org/web/20050302171708/http://members.chello.nl/p.cooijmans/gliaweb/tests/num.html">Numbers</a>, Item 18.

%H Paul Cooijmans, <a href="http://web.archive.org/web/20031006141136/http://members.chello.nl/p.cooijmans/gliaweb/tests/tfg/tfgshort.html">Short Test For Genius</a>, Item 29.

%t Prime[2^Range[0,30]]-1 (* _Harvey P. Dale_, Sep 30 2016 *)

%Y Equals A033844 - 1. Cf. A000040, A033844, A051438, A051440, A051439.

%K nonn,easy

%O 0,2

%A _N. J. A. Sloane_.