How-many-four-digit-numbers-are-there-whose-decimal-notation-contains-not-more-than-two-distinct-digits-

Question Number 21651 by Tinkutara last updated on 30/Sep/17

H o w m a n y f o u r - d i g i t n u m b e r s a r e

t h e r e w h o s e d e c i m a l n o t a t i o n c o n t a i n s

n o t m o r e t h a n t w o d i s t i n c t d i g i t s ?

Commented by mrW1 last updated on 01/Oct/17

576 ?

Commented by Tinkutara last updated on 02/Oct/17

Yes . Now I got it .

Commented by mrW1 last updated on 05/Oct/17

see Q 21693

\frac{9}{10} \times C_{2}^{10} \times 2! \times {_{2}^{4}} + 9 = \frac{9}{10} \times 45 \times 2 \times 7 + 9

= 567 + 9 = 576

Commented by Tinkutara last updated on 05/Oct/17

Can you explain what is stirling

function and where it is used ?