21979943 has 2 divisors, whose sum is σ = 21979944. Its totient is φ = 21979942.

The previous prime is 21979939. The next prime is 21979949. The reversal of 21979943 is 34997912.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21979943 - 2² = 21979939 is a prime.

It is a Sophie Germain prime.

It is a junction number, because it is equal to n+sod(n) for n = 21979894 and 21979903.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21979949) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10989971 + 10989972.

It is an arithmetic number, because the mean of its divisors is an integer number (10989972).

Almost surely, 2^21979943 is an apocalyptic number.

21979943 is a deficient number, since it is larger than the sum of its proper divisors (1).

21979943 is an equidigital number, since it uses as much as digits as its factorization.

21979943 is an evil number, because the sum of its binary digits is even.

The product of its digits is 122472, while the sum is 44.

The square root of 21979943 is about 4688.2771889043. The cubic root of 21979943 is about 280.1187548981.

It can be divided in two parts, 21979 and 943, that added together give a palindrome (22922).

The spelling of 21979943 in words is "twenty-one million, nine hundred seventy-nine thousand, nine hundred forty-three".