Narcissistic decimal number: Difference between revisions

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A [http://mathworld.wolfram.com/NarcissisticNumber.html Narcissistic decimal number] is a positice decimal number, <math>n</math> in which if there are <math>m</math> digits in the number then the sum of all the individual digits of the number raised to the power <math>m</math> is equal to <math>n</math>.
A [http://mathworld.wolfram.com/NarcissisticNumber.html Narcissistic decimal number] is a positive decimal number, <math>n</math> in which if there are <math>m</math> digits in the number then the sum of all the individual digits of the number raised to the power <math>m</math> is equal to <math>n</math>.


For example, if <math>n</math> is 153 then <math>m</math>, the number of digits is 3 and we have <math>1^3+5^3+3^3 = 1+125+27 = 153</math> and so 153 is a narcissistic decimal number.
For example, if <math>n</math> is 153 then <math>m</math>, the number of digits is 3 and we have <math>1^3+5^3+3^3 = 1+125+27 = 153</math> and so 153 is a narcissistic decimal number.

Revision as of 23:42, 6 March 2014

Narcissistic decimal number is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

A Narcissistic decimal number is a positive decimal number, in which if there are digits in the number then the sum of all the individual digits of the number raised to the power is equal to .

For example, if is 153 then , the number of digits is 3 and we have and so 153 is a narcissistic decimal number.

The task is to generate and show here, the first 25 narcissistic numbers.

Perl 6

Here is a straightforward, naive implementation. It works but takes ages. <lang perl6>sub is-narcissistic(Int $n) { $n == [+] $n.comb »**» $n.chars }

for 0 .. * {

   if .&is-narcissistic {

.say; last if ++state$ >= 25;

   }

}</lang>

Output:
0
1
2
3
4
5
6
7
8
9
153
370
371
407
Ctrl-C

Here the program was interrupted but if you're patient enough you'll see all the 25 numbers.

Python

This solution pre-computes the powers once.

<lang python>from __future__ import print_function from itertools import count, islice

def narcissists():

   for digits in count(0):
       digitpowers = [i**digits for i in range(10)]
       for n in range(int(10**(digits-1)), 10**digits):
           div, digitpsum = n, 0
           while div:
               div, mod = divmod(div, 10)
               digitpsum += digitpowers[mod]
           if n == digitpsum:
               yield n

for i, n in enumerate(islice(narcissists(), 25), 1):

   print(n, end=' ')
   if i % 5 == 0: print() 

print()</lang>

Output:
0 1 2 3 4 
5 6 7 8 9 
153 370 371 407 1634 
8208 9474 54748 92727 93084 
548834 1741725 4210818 9800817 9926315