21001040 has 20 divisors (see below), whose sum is σ = 48827604. Its totient is φ = 8400384.

The previous prime is 21001037. The next prime is 21001049. The reversal of 21001040 is 4010012.

It can be written as a sum of positive squares in 2 ways, for example, as 11316496 + 9684544 = 3364^2 + 3112^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a Harshad number since it is a multiple of its sum of digits (8).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001049) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 131177 + ... + 131336.

Almost surely, 2^21001040 is an apocalyptic number.

21001040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21001040 is an abundant number, since it is smaller than the sum of its proper divisors (27826564).

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

21001040 is a wasteful number, since it uses less digits than its factorization.

21001040 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 262526 (or 262520 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 8.

The square root of 21001040 is about 4582.6891668539. The cubic root of 21001040 is about 275.8969719774.

Adding to 21001040 its reverse (4010012), we get a palindrome (25011052).

The spelling of 21001040 in words is "twenty-one million, one thousand, forty".