21720012 has 12 divisors (see below), whose sum is σ = 50680056. Its totient is φ = 7240000.

The previous prime is 21720007. The next prime is 21720047. The reversal of 21720012 is 21002712.

It is a tau number, because it is divible by the number of its divisors (12).

It is a junction number, because it is equal to n+sod(n) for n = 21719973 and 21720000.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 904989 + ... + 905012.

It is an arithmetic number, because the mean of its divisors is an integer number (4223338).

Almost surely, 2^21720012 is an apocalyptic number.

It is an amenable number.

21720012 is an abundant number, since it is smaller than the sum of its proper divisors (28960044).

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

21720012 is a wasteful number, since it uses less digits than its factorization.

21720012 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1810008 (or 1810006 counting only the distinct ones).

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

The square root of 21720012 is about 4660.4733665155. The cubic root of 21720012 is about 279.0101613699.

Adding to 21720012 its reverse (21002712), we get a palindrome (42722724).

The spelling of 21720012 in words is "twenty-one million, seven hundred twenty thousand, twelve".