A022761 - OEIS

%I #10 May 26 2020 11:20:06

%S 24,64,104,136,168,192,240,320,384,408,448,480,536,576,616,672,720,

%T 792,816,840,952,1008,1040,1072,1088,1120,1240,1280,1392,1416,1528,

%U 1584,1624,1680,1760,1792,1840,1896,1944,1968,2064,2112,2144,2224

%N n-th 8k+1 prime plus n-th 8k+7 prime.

%H Harvey P. Dale, <a href="/A022761/b022761.txt">Table of n, a(n) for n = 1..1000</a>

%e The first four primes of the form 8k - 1 are 7, 23, 31, 47. The first four primes of the form 8k + 1 are 17, 41, 73, 89.

%e Thus a(1) = 7 + 17  = 24.

%e a(2) = 23 + 41 = 64.

%e a(3) = 31 + 73 = 104.

%e a(4) = 47 + 89 = 136.

%t thresh = 100; A007522 = Select[8Range[thresh] - 1, PrimeQ]; A007519 = Select[8Range[thresh] + 1, PrimeQ]; preExh = Min[Length[A007522], Length[A007519]]; Take[A007522, preExh] + Take[A007519, preExh]

%t Module[{nn=300,p1,p7,len},p1=Select[Prime[Range[nn]],IntegerQ[(#-1)/8]&];p7=Select[Prime[Range[nn]],IntegerQ[(#-7)/8]&];len=Min[ Length[ p1],Length[ p7]];Total/@Thread[{Take[p1,len],Take[p7,len]}]] (* _Harvey P. Dale_, May 26 2020 *)

%Y Cf. A007522, A007519.

%K nonn

%O 1,1

%A _Clark Kimberling_