Back to [Numbers 980-989]

 

[Library]  ISBN-987 and ISBN-950 are the International Standard Book Number codes for books published in Argentina.

 

[Math.]  The largest number of 3 different digits.

 

[Math.]  The 16th Fibonacci number.

 

[Math.]  A base system of multigrade equalities:               

             1+19+25 = 45 = 5+11+29 and

             12+192+252 = 987 = 52+112+292

Multigrade equalities still hold by adding any integer n to every base term in both sides.  Hence, the base equality always has number 1 appearing in one side.

 

[Math.]

9×9+(9–2) = 88

98×9+(9–3) = 888           

987×9+(9–4) = 8,888 

9,876×9+(9–5) = 88,888

98,765×9+(9–6) = 888,888

987,654×9+(9–7) = 8,888,888

9,876,543×9+(9–8) = 88,888,888

98,765,432×9+(9–9) = 888,888,888

987,654,321×9+(9–10) = 8,888,888,888

9,876,543,210×9+(9–11) = 88,888,888,888

98,765,432,099×9+(9–12) = 888,888,888,888  = 98,765,432,100×9–12.

...

 

[Math.]

 1×8+1 = 9

12×8+2 = 98

123×8+3 = 987

1234×8+4 = 9876

12,345×8+5 = 98,765

123,456×8+6 = 987,654

1,234,567×8+7 = 9,876,543

12,345,678×8+8 = 98,765,432

123,456,789×8+9 = 987,654,321

1,234,567,890×8+90 = 9,876,543,210

      (start of a new cycle)

12,345,678,901×8+901 = 98,765,432,109

123,456,789,012×8+9,002 = 987,654,321,098

1,234,567,890,123×8+90,003 = 9,876,543,210,987

12,345,678,901,234×8+900,004 = 98,765,432,109,876

123,456,789,012,345×8+9,000,005 = 987,654,321,098,765

1,234,567,890,123,456×8+90,000,006 = 9,876,543,210,987,654

12,345,678,901,234,567×8+900,000,007 = 98,765,432,109,876,543

123,456,789,012,345,678×8+9,000,000,008 = 987,654,321,098,765,432

1,234,567,890,123,456,789×8+90000000009 = 9,876,543,210,987,654,321

12,345,678,901,234,567,890×8+ 900000000090 = 98,765,432,109,876,543,210

... (end of cycle) ...

 

980-989

[Library]  Numbers 900-999 are the first 3 digits in Dewey Decimal Classification System call numbers for library books in History and Geography. Numbers 980-989 are for books in South American History.