All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Numbers > Sequences
Simple Sequence (Posted on 2007-05-07) Difficulty: 2 of 5
The sequence:

1, 3, 7, 13, 21, ...

What is the 600th member of the series?

What member, above the first, with fewer than 5 digits, is a perfect cube?

What member is a 5-digit palindrome that can also be read as a binary number?

What's the smaller of the two consecutive members that are 1000 apart?

See The Solution Submitted by Charlie    
Rating: 4.0000 (2 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution No Subject | Comment 3 of 7 |

f(x) = sigma(x+2) - 1 where x >= 0 and thus f(0) is the first number of the series.

f(599) = 359401
f(18) = 343 = 73
f(100) = 10101 <-- a palindromic "binary" number
            [f(4) = 21, in binary is also 10101;
             f(5) = 31, in binary is the five-digit palindrome 11111]
(499) = 249501; f(500) = 250501; f(500) - f(499) = 1000

Edited on May 7, 2007, 11:13 pm
  Posted by Dej Mar on 2007-05-07 20:51:19

Please log in:
Login:
Password:
Remember me:
Sign up! | Forgot password


Search:
Search body:
Forums (2)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (1)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Chatterbox:
Copyright © 2002 - 2020 by Animus Pactum Consulting. All rights reserved. Privacy Information