21213100021 has 4 divisors (see below), whose sum is σ = 22460929452. Its totient is φ = 19965270592.

The previous prime is 21213099967. The next prime is 21213100043. The reversal of 21213100021 is 12000131212.

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

It can be written as a sum of positive squares in 2 ways, for example, as 14474496100 + 6738603921 = 120310^2 + 82089^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21213100021 is a prime.

It is a super-2 number, since 2×21213100021² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21213099974 and 21213100010.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21213800021) 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, 623914690 + ... + 623914723.

It is an arithmetic number, because the mean of its divisors is an integer number (5615232363).

Almost surely, 2^21213100021 is an apocalyptic number.

It is an amenable number.

21213100021 is a deficient number, since it is larger than the sum of its proper divisors (1247829431).

21213100021 is a wasteful number, since it uses less digits than its factorization.

21213100021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1247829430.

The product of its (nonzero) digits is 24, while the sum is 13.

Adding to 21213100021 its reverse (12000131212), we get a palindrome (33213231233).

The spelling of 21213100021 in words is "twenty-one billion, two hundred thirteen million, one hundred thousand, twenty-one".