21172020 has 24 divisors (see below), whose sum is σ = 59281824. Its totient is φ = 5645856.

The previous prime is 21172009. The next prime is 21172037. The reversal of 21172020 is 2027112.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a congruent number.

It is an unprimeable number.

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, 176374 + ... + 176493.

It is an arithmetic number, because the mean of its divisors is an integer number (2470076).

Almost surely, 2^21172020 is an apocalyptic number.

21172020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21172020 is an abundant number, since it is smaller than the sum of its proper divisors (38109804).

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

21172020 is a wasteful number, since it uses less digits than its factorization.

21172020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 352879 (or 352877 counting only the distinct ones).

The product of its (nonzero) digits is 56, while the sum is 15.

The square root of 21172020 is about 4601.3063362484. The cubic root of 21172020 is about 276.6436877094.

Adding to 21172020 its reverse (2027112), we get a palindrome (23199132).

The spelling of 21172020 in words is "twenty-one million, one hundred seventy-two thousand, twenty".