21731257 has 2 divisors, whose sum is σ = 21731258. Its totient is φ = 21731256.

The previous prime is 21731243. The next prime is 21731263. The reversal of 21731257 is 75213712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21307456 + 423801 = 4616^2 + 651^2 .

It is a cyclic number.

It is not a de Polignac number, because 21731257 - 2²³ = 13342649 is a prime.

It is not a weakly prime, because it can be changed into another prime (21735257) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10865628 + 10865629.

It is an arithmetic number, because the mean of its divisors is an integer number (10865629).

Almost surely, 2^21731257 is an apocalyptic number.

It is an amenable number.

21731257 is a deficient number, since it is larger than the sum of its proper divisors (1).

21731257 is an equidigital number, since it uses as much as digits as its factorization.

21731257 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2940, while the sum is 28.

The square root of 21731257 is about 4661.6796329220. The cubic root of 21731257 is about 279.0583032704.

Adding to 21731257 its reverse (75213712), we get a palindrome (96944969).

The spelling of 21731257 in words is "twenty-one million, seven hundred thirty-one thousand, two hundred fifty-seven".