21247820 has 24 divisors (see below), whose sum is σ = 48677328. Its totient is φ = 7726400.

The previous prime is 21247819. The next prime is 21247823. The reversal of 21247820 is 2874212.

It is a self number, because there is not a number n which added to its sum of digits gives 21247820.

It is not an unprimeable number, because it can be changed into a prime (21247823) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 48071 + ... + 48510.

It is an arithmetic number, because the mean of its divisors is an integer number (2028222).

Almost surely, 2^21247820 is an apocalyptic number.

21247820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21247820 is an abundant number, since it is smaller than the sum of its proper divisors (27429508).

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

21247820 is a wasteful number, since it uses less digits than its factorization.

21247820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 96601 (or 96599 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 26.

The square root of 21247820 is about 4609.5357683828. The cubic root of 21247820 is about 276.9734407844.

The spelling of 21247820 in words is "twenty-one million, two hundred forty-seven thousand, eight hundred twenty".