21293257 has 2 divisors, whose sum is σ = 21293258. Its totient is φ = 21293256.

The previous prime is 21293191. The next prime is 21293263. The reversal of 21293257 is 75239212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18139081 + 3154176 = 4259^2 + 1776^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21293257 is a prime.

It is not a weakly prime, because it can be changed into another prime (21293057) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10646628 + 10646629.

It is an arithmetic number, because the mean of its divisors is an integer number (10646629).

Almost surely, 2^21293257 is an apocalyptic number.

It is an amenable number.

21293257 is a deficient number, since it is larger than the sum of its proper divisors (1).

21293257 is an equidigital number, since it uses as much as digits as its factorization.

21293257 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7560, while the sum is 31.

The square root of 21293257 is about 4614.4617237550. The cubic root of 21293257 is about 277.1707297653.

The spelling of 21293257 in words is "twenty-one million, two hundred ninety-three thousand, two hundred fifty-seven".