A117068 Decimal value of binary number whose n-th 1 is followed by n^2 0's.

5, 161, 164865, 21609185281, 1450167876173430785, 199309555259989211062227435521, 224402609700066672987369178785813291654447105

Offset

1,1

Comments

After a(1) = 5, when is a(n) prime?

Links

Table of n, a(n) for n=1..7.

Formula

a(n) = SUM[i=1,n] 2^(n+1).

Example

a(1) = 5 because 101 (base 2) = 5 (base 10).
a(2) = 161 because 10100001 (base 2) = 161 (base 10).
a(3) = 164865 because 101000010000000001 (base 2) = 164865 (base 10).

Mathematica

Table[FromDigits[Flatten[Join[{1}, Table[Join[PadRight[{}, n^2, 0], {1}], {n, i}]]], 2], {i, 8}] (* Harvey P. Dale, Mar 30 2016 *)

Crossrefs

Sequence in context: A229163 A322747 A274712 * A185832 A301667 A195950

Adjacent sequences: A117065 A117066 A117067 * A117069 A117070 A117071

Keyword

base,easy,nonn

Author

Jonathan Vos Post, Apr 16 2006

Status

approved