21966221 has 4 divisors (see below), whose sum is σ = 22380732. Its totient is φ = 21551712.

The previous prime is 21966209. The next prime is 21966233. The reversal of 21966221 is 12266912.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21966209) and next prime (21966233).

It can be written as a sum of positive squares in 2 ways, for example, as 8934121 + 13032100 = 2989^2 + 3610^2 .

It is a cyclic number.

It is not a de Polignac number, because 21966221 - 2¹⁸ = 21704077 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 (21966281) 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, 207176 + ... + 207281.

It is an arithmetic number, because the mean of its divisors is an integer number (5595183).

Almost surely, 2^21966221 is an apocalyptic number.

It is an amenable number.

21966221 is a deficient number, since it is larger than the sum of its proper divisors (414511).

21966221 is an equidigital number, since it uses as much as digits as its factorization.

21966221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 414510.

The product of its digits is 2592, while the sum is 29.

The square root of 21966221 is about 4686.8135230666. The cubic root of 21966221 is about 280.0604503835.

The spelling of 21966221 in words is "twenty-one million, nine hundred sixty-six thousand, two hundred twenty-one".