A154619 - OEIS

%I #10 Jan 12 2019 20:08:13

%S 23,71,167,191,479,743,1583,2039,2927,3863,5711,6551,7919,9767,10487,

%T 11423,15791,16703,18119,21647,21911,24359,27527,32159,35111,35447,

%U 38543,43991,45887,46271,52223,54287,55967,60719,67511,69383,76631

%N Primes of the form (4k^2 + 4k - 5)/5.

%C The numbers k that generate integers of the form (4k^2 + 4k - 5)/5 are in A047208. The primes are generated by the subset k = 5, 9, 14, 15, 24, 30, ... of these. - _R. J. Mathar_, Jan 25 2009

%H Vincenzo Librandi, <a href="/A154619/b154619.txt">Table of n, a(n) for n = 1..1000</a>

%p a := proc (n) if type((4/5)*n^2+(4/5)*n-1, integer) = true and isprime((4/5)*n^2+(4/5)*n-1) = true then (4/5)*n^2+(4/5)*n-1 else end if end proc: seq(a(n), n = 1 .. 340); # _Emeric Deutsch_, Jan 21 2009

%t Select[Table[(4n^2+4n-5)/5,{n,3,200}],PrimeQ] (* _Vincenzo Librandi_, Jul 23 2012 *)

%Y Cf. A028880.

%K nonn,easy

%O 1,1

%A _Vincenzo Librandi_, Jan 16 2009

%E Definition corrected and more terms from _R. J. Mathar_ and _Omar E. Pol_, Jan 24 2009

%E Extended by _Emeric Deutsch_, Jan 21 2009