A117011 Decimal value of binary number whose n-th 1 is followed by n^3 0's.

0, 5, 2561, 687463202817, 25362915524915764560280676204545, 2157638231708538191934637891565042782652856782390367212752413267066881

Offset

0,2

Comments

After a(1) = 5, the next prime is a(6), which has 135 digits (base 10).

Links

Table of n, a(n) for n=0..5.

Formula

a(0) = 0, for positive n: a(n+1) = 1 + a(n)*2^(1+n^3).

Example

a(1) = 5 because 101 (base 2) = 1 + 2^2 = 5 (base 10).
a(2) = 2561 because 101000000001 (base 2) = 1 + (1 + 2^2) * 2^9 = 2561 (base 10).
a(3) = 1 + (1 + (1 + 2^2) * 2^9) * 2^28.
a(4) = 1 + (1 + (1 + (1 + (2^2)) * (2^9)) * 2^28) * 2^65.
a(5) = 1 + (1 + (1 + (1 + (1 + (2^2)) * (2^9)) * 2^28) * 2^65) * 2^126.
a(6) = 1 + (1 + (1 + (1 + (1 + (1 + (2^2)) * (2^9)) * 2^28) * 2^65) * 2^126) * 2^217.

Crossrefs

Sequence in context: A346655 A114716 A036772 * A367957 A274527 A258980

Adjacent sequences: A117008 A117009 A117010 * A117012 A117013 A117014

Keyword

base,easy,nonn

Author

Jonathan Vos Post, Apr 16 2006

Status

approved