21780079 has 2 divisors, whose sum is σ = 21780080. Its totient is φ = 21780078.

The previous prime is 21780067. The next prime is 21780097. The reversal of 21780079 is 97008712.

Together with next prime (21780097) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21780079 - 2⁵ = 21780047 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21780779) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10890039 + 10890040.

It is an arithmetic number, because the mean of its divisors is an integer number (10890040).

Almost surely, 2^21780079 is an apocalyptic number.

21780079 is a deficient number, since it is larger than the sum of its proper divisors (1).

21780079 is an equidigital number, since it uses as much as digits as its factorization.

21780079 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7056, while the sum is 34.

The square root of 21780079 is about 4666.9132196774. The cubic root of 21780079 is about 279.2671268156.

The spelling of 21780079 in words is "twenty-one million, seven hundred eighty thousand, seventy-nine".