21213961 has 4 divisors (see below), whose sum is σ = 21344272. Its totient is φ = 21083652.

The previous prime is 21213947. The next prime is 21213971. The reversal of 21213961 is 16931212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21213961 - 2⁹ = 21213449 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21213901) by changing a digit.

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, 64911 + ... + 65236.

It is an arithmetic number, because the mean of its divisors is an integer number (5336068).

Almost surely, 2^21213961 is an apocalyptic number.

It is an amenable number.

21213961 is a deficient number, since it is larger than the sum of its proper divisors (130311).

21213961 is a wasteful number, since it uses less digits than its factorization.

21213961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 130310.

The product of its digits is 648, while the sum is 25.

The square root of 21213961 is about 4605.8615914940. The cubic root of 21213961 is about 276.8262409063.

The spelling of 21213961 in words is "twenty-one million, two hundred thirteen thousand, nine hundred sixty-one".