A013604 a(n) = 3^n - prevprime(3^n), where prevprime(x) is the largest prime < x.

1, 2, 4, 2, 2, 2, 8, 8, 2, 20, 16, 58, 22, 8, 16, 98, 10, 10, 14, 8, 4, 2, 20, 28, 20, 20, 26, 22, 14, 26, 4, 34, 52, 56, 28, 10, 2, 10, 58, 38, 2, 122, 74, 34, 22, 22, 46, 44, 50, 46, 16, 124, 4, 10, 106, 10, 26, 220, 38, 160, 74, 8, 28, 104, 104, 38, 298, 94, 16

Offset: 1

Author

James Kilfiger (mapdn(AT)csv.warwick.ac.uk)

Keywords

• nonn

Links

• Zak Seidov, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000244, A013598, A049711.

Programs

Magma

[3^n-PreviousPrime(3^n): n in [1..70]]; // Vincenzo Librandi, Sep 16 2016

Maple

seq(3^i-prevprime(3^i),i=1..100);

Mathematica

Table[3^i - NextPrime[3^i, - 1], {i, 70}] (* Vincenzo Librandi, Sep 16 2016 *)

PARI

a(n) = 3^n - precprime(3^n-1); \\ Michel Marcus, Sep 16 2016

Formula

a(n) = A049711(3^n) = A049711(A000244(n)). - Michel Marcus, Sep 16 2016