21021312440 has 16 divisors (see below), whose sum is σ = 47297953080. Its totient is φ = 8408524960.

The previous prime is 21021312437. The next prime is 21021312457. The reversal of 21021312440 is 4421312012.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a congruent number.

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, 262766366 + ... + 262766445.

Almost surely, 2^21021312440 is an apocalyptic number.

21021312440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21021312440 is an abundant number, since it is smaller than the sum of its proper divisors (26276640640).

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

21021312440 is a wasteful number, since it uses less digits than its factorization.

21021312440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 525532822 (or 525532818 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 20.

Adding to 21021312440 its reverse (4421312012), we get a palindrome (25442624452).

The spelling of 21021312440 in words is "twenty-one billion, twenty-one million, three hundred twelve thousand, four hundred forty".