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a(n) is the least prime >= 2^(2^n).
2

%I #18 Nov 18 2019 10:37:29

%S 2,5,17,257,65537,4294967311,18446744073709551629,

%T 340282366920938463463374607431768211507,

%U 115792089237316195423570985008687907853269984665640564039457584007913129640233

%N a(n) is the least prime >= 2^(2^n).

%C The next term has 155 digits. - _Harvey P. Dale_, Aug 31 2016

%C For further terms, consult A097521 or A129786. - _Jeppe Stig Nielsen_, Nov 18 2019

%p 2,seq(nextprime(2^(2^n)),n=1..8); # _Emeric Deutsch_, Nov 26 2007

%t Join[{2},NextPrime/@(2^(2^Range[8]))] (* _Harvey P. Dale_, Aug 31 2016 *)

%Y Cf. A019434, A097521, A129786.

%K nonn

%O 0,1

%A _Leroy Quet_, Nov 05 2007

%E More terms from _Emeric Deutsch_, Nov 26 2007