21781642279 has 2 divisors, whose sum is σ = 21781642280. Its totient is φ = 21781642278.

The previous prime is 21781642249. The next prime is 21781642291. The reversal of 21781642279 is 97224618712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21781642279 - 2⁹ = 21781641767 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21781642249) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10890821139 + 10890821140.

It is an arithmetic number, because the mean of its divisors is an integer number (10890821140).

Almost surely, 2^21781642279 is an apocalyptic number.

21781642279 is a deficient number, since it is larger than the sum of its proper divisors (1).

21781642279 is an equidigital number, since it uses as much as digits as its factorization.

21781642279 is an evil number, because the sum of its binary digits is even.

The product of its digits is 677376, while the sum is 49.

The spelling of 21781642279 in words is "twenty-one billion, seven hundred eighty-one million, six hundred forty-two thousand, two hundred seventy-nine".