21919820 has 24 divisors (see below), whose sum is σ = 49573104. Its totient is φ = 8093376.

The previous prime is 21919811. The next prime is 21919823. The reversal of 21919820 is 2891912.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (21919823) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 41894 + ... + 42413.

It is an arithmetic number, because the mean of its divisors is an integer number (2065546).

Almost surely, 2^21919820 is an apocalyptic number.

21919820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21919820 is an abundant number, since it is smaller than the sum of its proper divisors (27653284).

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

21919820 is a wasteful number, since it uses less digits than its factorization.

21919820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 84329 (or 84327 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 32.

The square root of 21919820 is about 4681.8607412011. The cubic root of 21919820 is about 279.8631133618.

It can be divided in two parts, 21 and 919820, that multiplied together give a triangular number (19316220 = T₆₂₁₅).

The spelling of 21919820 in words is "twenty-one million, nine hundred nineteen thousand, eight hundred twenty".