A246956 Numbers a(n) = 2^(n-1) * f(n), where n >= 1 and f(n) is the smallest prime number larger than 2^n (A014210).

3, 10, 44, 136, 592, 2144, 8384, 32896, 133376, 527872, 2102272, 8394752, 33624064, 134438912, 536920064, 2147516416, 8591835136, 34360131584, 137444458496, 549759483904, 2199041081344, 8796124479488, 35184409837568, 140737849065472, 562950540623872, 2251800317001728, 9007201200898048, 36028797421617152, 144115191028645888, 576460753914036224, 2305843021024854016, 9223372069067030528

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

Cf. A000203, A014210, A237270, A237271, A237593, A246955.

Sequence in context: A179501 A041737 A279105 * A026682 A335635 A096804

Adjacent sequences: A246953 A246954 A246955 * A246957 A246958 A246959

Keyword

nonn

Author

Hartmut F. W. Hoft, Sep 08 2014

Status

approved