21951990 has 24 divisors (see below), whose sum is σ = 57075408. Its totient is φ = 5853840.

The previous prime is 21951977. The next prime is 21951991. The reversal of 21951990 is 9915912.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21951991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 121866 + ... + 122045.

It is an arithmetic number, because the mean of its divisors is an integer number (2378142).

Almost surely, 2^21951990 is an apocalyptic number.

21951990 is an abundant number, since it is smaller than the sum of its proper divisors (35123418).

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

21951990 is a wasteful number, since it uses less digits than its factorization.

21951990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 243924 (or 243921 counting only the distinct ones).

The product of its (nonzero) digits is 7290, while the sum is 36.

The square root of 21951990 is about 4685.2950814223. The cubic root of 21951990 is about 279.9999574830. Note that the first 4 decimals are identical.

The spelling of 21951990 in words is "twenty-one million, nine hundred fifty-one thousand, nine hundred ninety".