Number 72

A page of the Numeropedia - the Special Encyclopedia of Numbers

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[Chemistry]  The atomic number of Hafnium (Hf).

 

[Chemistry]  The number of electrons that can reside in a shell is 2n2, i.e., 2, 8, 18, 32, 50, 72 and 98.

 

[History]  The number of years that U.S. law requires information collected in a U.S. census must remain confidential.

 

[Math.]  723 = 373,248  = (37+3+24+8)3

724 = 26,873,856  = (2+6+8+7+38+5+6)4

725 = 1,934,917,632  = (1+9+3+4+9+1+7+6+32)5

726 = 139,314,069,504  = (1+39+3+1+4+0+6+9+5+0+4)6

727 = 10,030,613,004,288 = (1+0+0+3+0+6+1+3+0+0+42+8+8)7

728 = 722,204,136,308,736 = (7+2+2+20+4+1+3+6+3+0+8+7+3+6)8.

 

[Math.]  72 = 24×3 and, reversely, 27 = 24+3.

 

[Math.]  The isosceles triangle with 3 angles (36o, 72o, 72o) is called a golden triangle, since its sides possess the golden ratio ½(1+51/2).

 

[Math.]  The smallest 5th power that can be expressed as the sum of five 5th powers, (Lander & Parkin, 1966): 1,934,917,632 = 725 = 675+475+465+435+195.

 

[Math.]  "Rule of 69", "Rule of 70" and "Rule of 72" are used in accounting to compute the time interval for a principal to double for a compound interest rate r. Since t = ln2/ln(1+r) = 0.693147/r, those rules state that value of t can be approximated by 0.69/r for low interest rates or more calculating-conveniently 0.70/r or 0.72/r for higher typical rates (such 5% to 10%).

 

[Math.]  Inserting 72 between 2 digits 2 in the square number 225 = 152 and repeatedly inserting numbers 72 between the digits 7 and 2 yields other squares 27225 = 1652, 2772225  = 16652, 277722225 = 166652, 27777222225 = 1666652, 2777772222225 = 16666652...

 

[Math.]

987,654,321×09 = 08,888,888,889

987,654,321×18 = 17,777,777,778

987,654,321×27 = 26,666,666,667

987,654,321×36 = 35,555,555,556

987,654,321×45 = 44,444,444,445

987,654,321×54 = 53,333,333,334

987,654,321×63 = 62,222,222,223

987,654,321×72 = 71,111,111,112

987,654,321×81 = 80,000,000,001.

 

 [Math.]  A base system of multigrade equalities: 

1+6+7+17+18+23 = 72 = 2+3+11+13+21+22

12+62+72+172+182+232 = 1,228 = 22+32+112+132+212+222

13+63+73+173+183+233 = 23,472 = 23+33+113+133+213+223

14+64+74+174+184+234 = 472,036 = 24+34+114+134+214+224

15+65+75+175+185+235 = 9,770,352= 25+35+115+135+215+225. (References [??])

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

 

[Measure]  The number of points in one inch.

Point is a unit used in printing for measuring type/font size (the height of capital letters). Pica is a unit used in printing for measuring column width: 1 inch = 6 picas = 72 points.

 

[Science]  The number of points in one inch.

Point is a unit used in printing for measuring type/font size (the height of capital letters).

 

[Science]  The number 1039 is duodecillion, in American system. In British system, duodecillion is 1072.

 

[Science] Fujita Scale for Tornado

Scale, Intensity

Wind Speed

F0, Gale

40-72 mph

F1, Moderate

73-112 mph

F4, Devastating

207-260 mph

F2, Significant

113-157 mph

F5, Incredible

261-318 mph

F3, Severe

158-206 mph

F6, Inconceivable

319-379 mph

 

[Sport]  The number of arrows shot by each competitor in an international archery competitions.

 

[Sport]  The total number of holes played in four rounds of a professional golf tournament or championship.

 

[Sport]  The popular scores for an even par of an 18-hole round of a golf course are 70, 71 or 72.

 

[World]  The ISO country code for Botswanai is 072. (ISO-3166)