21731191 has 2 divisors, whose sum is σ = 21731192. Its totient is φ = 21731190.

The previous prime is 21731161. The next prime is 21731239. The reversal of 21731191 is 19113712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21731191 - 2¹¹ = 21729143 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21731111) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10865595 + 10865596.

It is an arithmetic number, because the mean of its divisors is an integer number (10865596).

Almost surely, 2^21731191 is an apocalyptic number.

21731191 is a deficient number, since it is larger than the sum of its proper divisors (1).

21731191 is an equidigital number, since it uses as much as digits as its factorization.

21731191 is an evil number, because the sum of its binary digits is even.

The product of its digits is 378, while the sum is 25.

The square root of 21731191 is about 4661.6725539231. The cubic root of 21731191 is about 279.0580207608.

It can be divided in two parts, 2173 and 1191, that added together give a square (3364 = 58²).

The spelling of 21731191 in words is "twenty-one million, seven hundred thirty-one thousand, one hundred ninety-one".