21720426 has 48 divisors (see below), whose sum is σ = 54429984. Its totient is φ = 5727456.

The previous prime is 21720409. The next prime is 21720427. The reversal of 21720426 is 62402712.

It is a junction number, because it is equal to n+sod(n) for n = 21720396 and 21720405.

It is not an unprimeable number, because it can be changed into a prime (21720427) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 981 + ... + 6663.

It is an arithmetic number, because the mean of its divisors is an integer number (1133958).

Almost surely, 2^21720426 is an apocalyptic number.

21720426 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 21720426, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27214992).

21720426 is an abundant number, since it is smaller than the sum of its proper divisors (32709558).

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

21720426 is a wasteful number, since it uses less digits than its factorization.

21720426 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5715 (or 5708 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 24.

The square root of 21720426 is about 4660.5177823929. The cubic root of 21720426 is about 279.0119340741.

The spelling of 21720426 in words is "twenty-one million, seven hundred twenty thousand, four hundred twenty-six".