21720620 has 12 divisors (see below), whose sum is σ = 45613344. Its totient is φ = 8688240.

The previous prime is 21720617. The next prime is 21720631. The reversal of 21720620 is 2602712.

It is a Harshad number since it is a multiple of its sum of digits (20), and also a Moran number because the ratio is a prime number: 1086031 = 21720620 / (2 + 1 + 7 + 2 + 0 + 6 + 2 + 0).

It is a junction number, because it is equal to n+sod(n) for n = 21720592 and 21720601.

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 3 ways as a sum of consecutive naturals, for example, 542996 + ... + 543035.

It is an arithmetic number, because the mean of its divisors is an integer number (3801112).

Almost surely, 2^21720620 is an apocalyptic number.

21720620 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21720620 is an abundant number, since it is smaller than the sum of its proper divisors (23892724).

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

21720620 is a wasteful number, since it uses less digits than its factorization.

21720620 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1086040 (or 1086038 counting only the distinct ones).

The product of its (nonzero) digits is 336, while the sum is 20.

The square root of 21720620 is about 4660.5385954844. The cubic root of 21720620 is about 279.0127647539.

The spelling of 21720620 in words is "twenty-one million, seven hundred twenty thousand, six hundred twenty".