21005431603 has 4 divisors (see below), whose sum is σ = 22621234048. Its totient is φ = 19389629160.

The previous prime is 21005431597. The next prime is 21005431613. The reversal of 21005431603 is 30613450012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21005431603 - 2⁵ = 21005431571 is a prime.

It is a super-2 number, since 2×21005431603² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21005431613) 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, 807901203 + ... + 807901228.

It is an arithmetic number, because the mean of its divisors is an integer number (5655308512).

Almost surely, 2^21005431603 is an apocalyptic number.

21005431603 is a deficient number, since it is larger than the sum of its proper divisors (1615802445).

21005431603 is a wasteful number, since it uses less digits than its factorization.

21005431603 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1615802444.

The product of its (nonzero) digits is 2160, while the sum is 25.

Adding to 21005431603 its reverse (30613450012), we get a palindrome (51618881615).

The spelling of 21005431603 in words is "twenty-one billion, five million, four hundred thirty-one thousand, six hundred three".