21651890 has 32 divisors (see below), whose sum is σ = 42287616. Its totient is φ = 7934400.

The previous prime is 21651881. The next prime is 21651907. The reversal of 21651890 is 9815612.

It is a Curzon number.

It is an unprimeable number.

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 in 15 ways as a sum of consecutive naturals, for example, 19079 + ... + 20181.

It is an arithmetic number, because the mean of its divisors is an integer number (1321488).

Almost surely, 2^21651890 is an apocalyptic number.

21651890 is a deficient number, since it is larger than the sum of its proper divisors (20635726).

21651890 is a wasteful number, since it uses less digits than its factorization.

21651890 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1274.

The product of its (nonzero) digits is 4320, while the sum is 32.

The square root of 21651890 is about 4653.1591419164. The cubic root of 21651890 is about 278.7181628261.

The spelling of 21651890 in words is "twenty-one million, six hundred fifty-one thousand, eight hundred ninety".