login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

a(n) = prime(n)*(prime(n-1) + prime(n+1)).
0

%I #63 Feb 08 2023 07:21:01

%S 21,50,112,220,364,544,760,1104,1566,2046,2664,3280,3784,4512,5618,

%T 6726,7686,8844,9940,10950,12324,13944,16020,18430,20200,21424,22684,

%U 23980,26668,30988,34584,36990,39754,43210,46206,49298,52812,56112,59858,63366,66970,71434,74884,77224,81192

%N a(n) = prime(n)*(prime(n-1) + prime(n+1)).

%C 21 is the only semiprime term.

%C All terms after 21 are even.

%F a(n) = A000040(n)*A048448(n).

%F a(n) = A006094(n) + A006094(n-1).

%t Array[Prime[# + 1] (Prime[#] + Prime[# + 2]) &, 45] (* _Michael De Vlieger_, Oct 09 2022 *)

%o (PARI) a(n) = prime(n)*(prime(n-1) + prime(n+1)) \\ _Michel Marcus_, Oct 09 2022

%Y Cf. A000040, A048448, A006094.

%Y Cf. A338529 (first differences).

%K nonn,easy

%O 2,1

%A _Saish S. Kambali_, Oct 09 2022