2.7182818284
The value of Pi is 3.14159, but the first 10 digits are 3.141592658
3.14159 2.71828
for (first=n; first>=10; first/=10);
I believe they are 3.1415926535
This is a computer's method of representing scientific numbers. The 'e' or 'E' means exponential and represents the "× 10" in the normal scientific representation. The digits before the 'e' are the mantissa; The digits after the 'e' are the exponent; for positive numbers the '+' is not necessary. Thus 5e+004 = 5 × 10⁺⁰⁰⁴ = 5 × 10⁴ (= 50,000)
There are 10 digits from which the first number can be selected, 10 digits from which the second number can be chosen and 10 from which the third number can be picked. This gives you a total number of combinations of 10 x 10 x 10 = 1000.
There are 10 digits. first there are three digits then space then another three then space and then the last four digits. (example: xxx xxx xxxx)
There are 10 digits in a billion.
To combine 2 digits, you can choose from the 10 digits available (0-9). If repetition is allowed, there are (10 \times 10 = 100) combinations. If repetition is not allowed, there are (10 \times 9 = 90) combinations, as you select the first digit and then choose a different second digit.
Two - the first three zeros are not significant.
Since 0 cannot be in the first place of the 4-digits number, we have 9 x 10 x 10 x 10 = 9,000 combinations.
10 digits to select for the first number in the sequence 10 digits to select for the second number in the sequence for each possible option of 10 digits in the first slot in the sequence (10 * 10) 10 digits to select for the third number in the sequence for each possible option of 10 digits in the second slot for each possible digit in the first slot of the sequence (or more easily put, 10 possible digits for each of 100 potential first two number sequences) [10*10*10] etc.... =10 * 10 * 10 * 10 * 10 * 10 * 10 = 10^7 = 10,000,000 (10 Million) Now add an area code before that 7 digit phone number and you get 10 Billion combinations (of course there are exclusions such as any sequence starting in 911 would be prohibited which is a reduction of 10 million numbers itself - 911 000 0001, 911 000 0002, etc. There are many other exclusions as well such as can't start with 0 - this removes another 1 billion sequences)