21221242720 has 48 divisors (see below), whose sum is σ = 50984957520. Its totient is φ = 8344620544.

The previous prime is 21221242717. The next prime is 21221242733. The reversal of 21221242720 is 2724212212.

It is a happy number.

It is a super-2 number, since 2×21221242720² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1114567 + ... + 1133446.

It is an arithmetic number, because the mean of its divisors is an integer number (1062186615).

Almost surely, 2^21221242720 is an apocalyptic number.

21221242720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21221242720 is an abundant number, since it is smaller than the sum of its proper divisors (29763714800).

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

21221242720 is a wasteful number, since it uses less digits than its factorization.

21221242720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2248087 (or 2248079 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 25.

Adding to 21221242720 its reverse (2724212212), we get a palindrome (23945454932).

The spelling of 21221242720 in words is "twenty-one billion, two hundred twenty-one million, two hundred forty-two thousand, seven hundred twenty".