21256990 has 8 divisors (see below), whose sum is σ = 38262600. Its totient is φ = 8502792.

The previous prime is 21256931. The next prime is 21256997. The reversal of 21256990 is 9965212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21256997) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1062840 + ... + 1062859.

It is an arithmetic number, because the mean of its divisors is an integer number (4782825).

Almost surely, 2^21256990 is an apocalyptic number.

21256990 is a deficient number, since it is larger than the sum of its proper divisors (17005610).

21256990 is a wasteful number, since it uses less digits than its factorization.

21256990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2125706.

The product of its (nonzero) digits is 9720, while the sum is 34.

The square root of 21256990 is about 4610.5303382583. The cubic root of 21256990 is about 277.0132798700.

The spelling of 21256990 in words is "twenty-one million, two hundred fifty-six thousand, nine hundred ninety".