21720615 has 32 divisors (see below), whose sum is σ = 41005056. Its totient is φ = 9607680.

The previous prime is 21720613. The next prime is 21720617. The reversal of 21720615 is 51602712.

It is an interprime number because it is at equal distance from previous prime (21720613) and next prime (21720617).

It is not a de Polignac number, because 21720615 - 2¹ = 21720613 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21720613) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 82 + ... + 6591.

It is an arithmetic number, because the mean of its divisors is an integer number (1281408).

Almost surely, 2^21720615 is an apocalyptic number.

21720615 is a deficient number, since it is larger than the sum of its proper divisors (19284441).

21720615 is a wasteful number, since it uses less digits than its factorization.

21720615 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6719.

The product of its (nonzero) digits is 840, while the sum is 24.

The square root of 21720615 is about 4660.5380590657. The cubic root of 21720615 is about 279.0127433447.

The spelling of 21720615 in words is "twenty-one million, seven hundred twenty thousand, six hundred fifteen".