21709879 has 2 divisors, whose sum is σ = 21709880. Its totient is φ = 21709878.

The previous prime is 21709847. The next prime is 21709903. The reversal of 21709879 is 97890712.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21709879 - 2⁵ = 21709847 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21709819) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10854939 + 10854940.

It is an arithmetic number, because the mean of its divisors is an integer number (10854940).

Almost surely, 2^21709879 is an apocalyptic number.

21709879 is a deficient number, since it is larger than the sum of its proper divisors (1).

21709879 is an equidigital number, since it uses as much as digits as its factorization.

21709879 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 63504, while the sum is 43.

The square root of 21709879 is about 4659.3861183637. The cubic root of 21709879 is about 278.9667659099.

The spelling of 21709879 in words is "twenty-one million, seven hundred nine thousand, eight hundred seventy-nine".