21013020 has 240 divisors, whose sum is σ = 80498880. Its totient is φ = 4478976.

The previous prime is 21013019. The next prime is 21013021. The reversal of 21013020 is 2031012.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21013019) and next prime (21013021).

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a junction number, because it is equal to n+sod(n) for n = 21012993 and 21013011.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21013021) by changing a digit.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 192726 + ... + 192834.

It is an arithmetic number, because the mean of its divisors is an integer number (335412).

Almost surely, 2^21013020 is an apocalyptic number.

21013020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21013020, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40249440).

21013020 is an abundant number, since it is smaller than the sum of its proper divisors (59485860).

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

21013020 is a wasteful number, since it uses less digits than its factorization.

21013020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 154 (or 143 counting only the distinct ones).

The product of its (nonzero) digits is 12, while the sum is 9.

The square root of 21013020 is about 4583.9960732967. The cubic root of 21013020 is about 275.9494236248.

Adding to 21013020 its reverse (2031012), we get a palindrome (23044032).

The spelling of 21013020 in words is "twenty-one million, thirteen thousand, twenty".