屑俺日記

☆ 2n + 1

Rubyの教科書(まだ版元に情報がない)に出ていた、 の累計( (0 * 2 +1) + (1 * 2 +1) + (2 * 2 + 1) + ... (n * 2 + 1)
が、(n + 1) ** 2 になるって話。

import sys
last = int(sys.argv[1])
 
def raising(last):
  sum = 0
  for x in range(last + 1):
    num = 2 * x + 1
    sum += num
  print(repr(x).rjust(2),
    repr(num).rjust(5),
    repr(sum).rjust(4),
    repr((last + 1)** 2).rjust(10))
 
print(' n  2n+1  sum   (n+1)**2')
for x in range(last + 1):
  raising(x)

$ python3 hoge.py 12
 n  2n+1  sum   (n+1)**2
 0     1    1          1
 1     3    4          4
 2     5    9          9
 3     7   16         16
 4     9   25         25
 5    11   36         36
 6    13   49         49
 7    15   64         64
 8    17   81         81
 9    19  100        100
10    21  121        121
11    23  144        144
12    25  169        169

☆ 目当てはOpenSSH-5.6p1 だったんだけど

ftp サイトに入った途端、

ncftp /pub > cd OpenBSD
 
 Welcome to ftp.eu.OpenBSD.org 
 Located at the Stockholm University
 Department of IT & Media
 For other mirror sites visit http://www.openbsd.org/ftp.html
      _____                 ____   _____ _____   
     / ___ \               |  _ \ / ____|  __ \  
    / /  / /___  ___  ____ | |_) | (___ | |  | | 
   / /  / / __ \/ _ \/ __ \|  _ < \___ \| |  | | 
  / /__/ / /_/ /  __/ / / /| |_) |____) | |__| | 
  \_____/ .___/\___/_/ /_/ |____/|_____/|_____/  
       /_/                                       
              |    .            The proactively secure Unix-like
          .   |L  /|   .        Operating System.
      _ . |\ _| \--+._/| .      Please visit the OpenBSD web site
     / ||\| Y J  )   / |/| ./   at http://www.openbsd.org/
    J  |)'( |        ` F`.'/
  -<|  F         __     .-<     All transfers are logged, if you don't
    | /       .-'. `.  /-. L___ like this policy, disconnect now!
    J \      <    \  | | O\|.-' 
  _J \  .-    \/ O | | \  |F    
 '-F  -<_.     \   .-'  `-' L__
__J  _   _.     >-'  )._.   |-' You can order OpenBSD CDROMs
`-|.'   /_.           \_|   F   from http://www.openbsd.org/orders.html.
  /.-   .                _.<    CD sales are important to support the   
 /'    /.'             .'  `\   continued development of the project.   
  /L  /'   |/      _.-'-\      
 /'J       ___.---'\|          
   |\  .--' V  | `. `          
   |/`. `-.     `._)           
      / .-.\                   
VK    \ (  `\                  
       `.\                     
Directory successfully changed.