21781642291 has 2 divisors, whose sum is σ = 21781642292. Its totient is φ = 21781642290.

The previous prime is 21781642279. The next prime is 21781642403. The reversal of 21781642291 is 19224618712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21781642291 - 2⁷ = 21781642163 is a prime.

It is not a weakly prime, because it can be changed into another prime (21781642891) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10890821145 + 10890821146.

It is an arithmetic number, because the mean of its divisors is an integer number (10890821146).

Almost surely, 2^21781642291 is an apocalyptic number.

21781642291 is a deficient number, since it is larger than the sum of its proper divisors (1).

21781642291 is an equidigital number, since it uses as much as digits as its factorization.

21781642291 is an evil number, because the sum of its binary digits is even.

The product of its digits is 96768, while the sum is 43.

The spelling of 21781642291 in words is "twenty-one billion, seven hundred eighty-one million, six hundred forty-two thousand, two hundred ninety-one".