21257740 has 24 divisors (see below), whose sum is σ = 51018912. Its totient is φ = 7288320.

The previous prime is 21257737. The next prime is 21257749. The reversal of 21257740 is 4775212.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a junction number, because it is equal to n+sod(n) for n = 21257699 and 21257708.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21257749) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 75781 + ... + 76060.

It is an arithmetic number, because the mean of its divisors is an integer number (2125788).

Almost surely, 2^21257740 is an apocalyptic number.

21257740 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21257740 is an abundant number, since it is smaller than the sum of its proper divisors (29761172).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21257740 is a wasteful number, since it uses less digits than its factorization.

21257740 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 151857 (or 151855 counting only the distinct ones).

The product of its (nonzero) digits is 3920, while the sum is 28.

The square root of 21257740 is about 4610.6116730863. The cubic root of 21257740 is about 277.0165377398.

The spelling of 21257740 in words is "twenty-one million, two hundred fifty-seven thousand, seven hundred forty".