21205279 has 2 divisors, whose sum is σ = 21205280. Its totient is φ = 21205278.

The previous prime is 21205243. The next prime is 21205291. The reversal of 21205279 is 97250212.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21205279 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21205879) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10602639 + 10602640.

It is an arithmetic number, because the mean of its divisors is an integer number (10602640).

Almost surely, 2^21205279 is an apocalyptic number.

21205279 is a deficient number, since it is larger than the sum of its proper divisors (1).

21205279 is an equidigital number, since it uses as much as digits as its factorization.

21205279 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2520, while the sum is 28.

The square root of 21205279 is about 4604.9190003734. The cubic root of 21205279 is about 276.7884712293.

It can be divided in two parts, 21205 and 279, that multiplied together give a palindrome (5916195).

The spelling of 21205279 in words is "twenty-one million, two hundred five thousand, two hundred seventy-nine".