21720220542 has 12 divisors (see below), whose sum is σ = 47060477880. Its totient is φ = 7240073508.

The previous prime is 21720220537. The next prime is 21720220547. The reversal of 21720220542 is 24502202712.

21720220542 is a `hidden beast` number, since 217 + 202 + 205 + 42 = 666.

It is an interprime number because it is at equal distance from previous prime (21720220537) and next prime (21720220547).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21720220547) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 603339442 + ... + 603339477.

It is an arithmetic number, because the mean of its divisors is an integer number (3921706490).

Almost surely, 2^21720220542 is an apocalyptic number.

21720220542 is an abundant number, since it is smaller than the sum of its proper divisors (25340257338).

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

21720220542 is a wasteful number, since it uses less digits than its factorization.

21720220542 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1206678927 (or 1206678924 counting only the distinct ones).

The product of its (nonzero) digits is 4480, while the sum is 27.

The spelling of 21720220542 in words is "twenty-one billion, seven hundred twenty million, two hundred twenty thousand, five hundred forty-two".