# 247 (number)

247 (two hundred [and] forty-seven) is the natural number following 246 and preceding 248.

 ← 246 247 248 →
Cardinaltwo hundred forty-seven
Ordinal247th
(two hundred forty-seventh)
Factorization13 × 19
Greek numeralΣΜΖ´
Roman numeralCCXLVII
Binary111101112
Ternary1000113
Octal3678
Duodecimal18712

## In mathematics

247 is:

• a semiprime.
• a brilliant number (the product of two primes with the same number of digits).[1]
• a pentagonal number.[2]
• palindromic in bases 18 (DD18) and 246 (11246).
• a Harshad number in bases 10, 14, 19, 20, 27, 39, 40, 58, 77, 79, 115, 118, 229 and 235.
• the smallest number which can be expressed as the difference between two integers that contain together all digits 0–9. i.e. 247 = 50123 - 49876.[3]

The mathematician and philosopher Alex Bellos suggested in 2014 that a candidate for the lowest uninteresting number would be 247 because it was, at the time, "the lowest number not to have its own page on English Wikipedia".[4]

## In other fields

• Sometimes (e.g. when it is used in a URL), 247 is used as an alternative to 24/7, an abbreviation which means "24 hours a day, 7 days a week".
• Approximate number of acres in a square kilometer (1 km2 ≈ 247.10538 acres).

## References

1. ^ "Sloane's A078972 : Brilliant numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-28.
2. ^ "Sloane's A000326 : Pentagonal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-28.
3. ^ Friedman, Erich. "What's Special About This Number?". stetson.edu. Archived from the original on 23 February 2018. Retrieved 15 April 2016.
4. ^ Bellos, Alex (June 2014). The Grapes of Math: How Life Reflects Numbers and Numbers Reflect Life. illus. The Surreal McCoy (1st Simon & Schuster hardcover ed.). N.Y.: Simon & Schuster. pp. 238 & 319 (quoting p. 319). ISBN 978-1-4516-4009-0.