21897966 has 16 divisors (see below), whose sum is σ = 45209088. Its totient is φ = 7063800.

The previous prime is 21897949. The next prime is 21898007. The reversal of 21897966 is 66979812.

Added to its reverse (66979812) it gives a triangular number (88877778 = T₁₃₃₃₂).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 58680 + ... + 59051.

It is an arithmetic number, because the mean of its divisors is an integer number (2825568).

Almost surely, 2^21897966 is an apocalyptic number.

21897966 is an abundant number, since it is smaller than the sum of its proper divisors (23311122).

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

21897966 is a wasteful number, since it uses less digits than its factorization.

21897966 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 117767.

The product of its digits is 326592, while the sum is 48.

The square root of 21897966 is about 4679.5262580736. The cubic root of 21897966 is about 279.7700748515.

Adding to 21897966 its reverse (66979812), we get a triangular number (88877778 = T₁₃₃₃₂).

The spelling of 21897966 in words is "twenty-one million, eight hundred ninety-seven thousand, nine hundred sixty-six".