21005402420 has 12 divisors (see below), whose sum is σ = 44111345124. Its totient is φ = 8402160960.

The previous prime is 21005402401. The next prime is 21005402459. The reversal of 21005402420 is 2420450012.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 5687874724 + 15317527696 = 75418^2 + 123764^2 .

It is a super-2 number, since 2×21005402420² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (20), and also a Moran number because the ratio is a prime number: 1050270121 = 21005402420 / (2 + 1 + 0 + 0 + 5 + 4 + 0 + 2 + 4 + 2 + 0).

It is a junction number, because it is equal to n+sod(n) for n = 21005402392 and 21005402401.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 525135041 + ... + 525135080.

It is an arithmetic number, because the mean of its divisors is an integer number (3675945427).

Almost surely, 2^21005402420 is an apocalyptic number.

21005402420 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21005402420 is an abundant number, since it is smaller than the sum of its proper divisors (23105942704).

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

21005402420 is a wasteful number, since it uses less digits than its factorization.

21005402420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1050270130 (or 1050270128 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 20.

Adding to 21005402420 its reverse (2420450012), we get a palindrome (23425852432).

The spelling of 21005402420 in words is "twenty-one billion, five million, four hundred two thousand, four hundred twenty".