Take the 2-minute tour ×
MathOverflow is a question and answer site for professional mathematicians. It's 100% free, no registration required.

I'm trying to understand the formula presented for the sequence A064532 from the OEIS, looks like a recurrence relation with complex numbers:

$a(10i+j) = a(i) + a(j), etc.$

Sorry if its a simple equation, but I wasn't able to understand it.

share|improve this question
add comment

1 Answer

up vote 2 down vote accepted

Nothing to do with complex numbers.

Look at the number of holes in each digit

0 1 2 3 4 5 6 7 8 9
1 0 0 0 0 0 1 0 2 1

Now look at the total number of holes when you write the number in the usual way; just take the weighted sum of the digits.

share|improve this answer
    
Ok, so if I understood there is no "closed form" formula for a formula like a(8) = 2 for instance, right ? –  Tarantulae Apr 4 '12 at 17:10
    
Sorry my answer did not typeset properly. The digit 8 has two holes; just look at it. There is no formula for the number of holes in a digit. –  Bruce Westbury Apr 4 '12 at 17:30
2  
You will kick yourself when you get it! or as my children would say "facepalm"! –  Bruce Westbury Apr 4 '12 at 17:38
    
Thanks Bruce ! hheeh –  Tarantulae Apr 4 '12 at 17:44
2  
Edited only to align the table (insert quadruple space before each line). But it looks to me like the digit 9 has one hole, not zero.$$ $$I'm reminded of the GRE question I heard of last week(?): Which of the following shapes is simple connected? (A)a (B)b (C)c (D)d (E)e –  Noam D. Elkies Apr 4 '12 at 17:55
show 1 more comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.