OFFSET
1,1
COMMENTS
The sequence is the "diagonal" - first element in each column - of the triangle of numbers associated with the symmetric representation of sigma(n) when it has two parts, each of width one (see A246955).
LINKS
Jens Kruse Andersen, Table of n, a(n) for n = 1..1000
EXAMPLE
a(4) = 8 * 17 = 136 since 17 is the first prime larger than 16.
MATHEMATICA
f[n_] := Module[{v = 2^n + 1}, While[!PrimeQ[v], v++]; v]
a[n_] := 2^(n - 1) f[n]
Map[a, Range[32]] (* data *)
PROG
(PARI) a(n) = 2^(n-1) * nextprime(2^n+1); \\ Michel Marcus, Sep 23 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Hartmut F. W. Hoft, Sep 08 2014
STATUS
approved