# 881

This number is a prime. Hill 881 was the site of fierce and bloody fighting between soldiers of the North Vietnamese Army and United States Marines during the Vietnam War. The number refers to the elevation of the hill in meters. The binary digits extraction from the decimal expansion of π truncated to 10 places (1101110001) and converted to base 10 gives prime 881. [De Geest] The largest three-digit prime of any form ABC such that A + BC, AB + C, and A + B + C are prime. In the case of 881: 8 + 81; 88 + 1; and 8 + 8 + 1 are all prime. [Kilpatrick] There are 881 distinct Pythagorean triangles whose sides do not exceed a thousand. [Beedassy] The largest of only two prime numbers with squares of the form AABCBC. (The other is 577). [Loungrides] The smallest nontrivial (mutidigit) Sophie Germain prime p such that p-pi(p) is a perfect cube, i.e., (881-152 = 9^3). [Bajpai] The lesser of the largest known twin prime pair (881, 883) where both primes are near repdigit primes. [Gupta] The smallest prime p such that the concatenation of pi(p) and p {152||881} is a perfect square (152881 = 391^2). [Bajpai]

(There are 4 curios for this number that have not yet been approved by an editor.)