21951999 has 16 divisors (see below), whose sum is σ = 33571840. Its totient is φ = 14162040.

The previous prime is 21951997. The next prime is 21952003. The reversal of 21951999 is 99915912.

It is a Cunningham number, because it is equal to 280³-1.

It is not a de Polignac number, because 21951999 - 2¹ = 21951997 is a prime.

It is a Duffinian number.

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 (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 12277 + ... + 13950.

It is an arithmetic number, because the mean of its divisors is an integer number (2098240).

Almost surely, 2^21951999 is an apocalyptic number.

21951999 is a deficient number, since it is larger than the sum of its proper divisors (11619841).

21951999 is a wasteful number, since it uses less digits than its factorization.

21951999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26267 (or 26261 counting only the distinct ones).

The product of its digits is 65610, while the sum is 45.

The square root of 21951999 is about 4685.2960418740. The cubic root of 21951999 is about 279.9999957483. Note that the first 5 decimals are identical.

The spelling of 21951999 in words is "twenty-one million, nine hundred fifty-one thousand, nine hundred ninety-nine".