21720651546 has 32 divisors (see below), whose sum is σ = 47494277568. Its totient is φ = 6567603840.

The previous prime is 21720651541. The next prime is 21720651587. The reversal of 21720651546 is 64515602712.

It is a Smith number, since the sum of its digits (39) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is not an unprimeable number, because it can be changed into a prime (21720651541) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 329905 + ... + 390228.

It is an arithmetic number, because the mean of its divisors is an integer number (1484196174).

Almost surely, 2^21720651546 is an apocalyptic number.

21720651546 is an abundant number, since it is smaller than the sum of its proper divisors (25773626022).

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

21720651546 is a wasteful number, since it uses less digits than its factorization.

21720651546 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 720606.

The product of its (nonzero) digits is 100800, while the sum is 39.

The spelling of 21720651546 in words is "twenty-one billion, seven hundred twenty million, six hundred fifty-one thousand, five hundred forty-six".