21987287688649 has 2 divisors, whose sum is σ = 21987287688650. Its totient is φ = 21987287688648.

The previous prime is 21987287688617. The next prime is 21987287688671. The reversal of 21987287688649 is 94688678278912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21245093377600 + 742194311049 = 4609240^2 + 861507^2 .

It is a cyclic number.

It is not a de Polignac number, because 21987287688649 - 2⁵ = 21987287688617 is a prime.

It is not a weakly prime, because it can be changed into another prime (21987287688049) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10993643844324 + 10993643844325.

It is an arithmetic number, because the mean of its divisors is an integer number (10993643844325).

Almost surely, 2^{21987287688649} is an apocalyptic number.

It is an amenable number.

21987287688649 is a deficient number, since it is larger than the sum of its proper divisors (1).

21987287688649 is an equidigital number, since it uses as much as digits as its factorization.

21987287688649 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9364045824, while the sum is 85.

The spelling of 21987287688649 in words is "twenty-one trillion, nine hundred eighty-seven billion, two hundred eighty-seven million, six hundred eighty-eight thousand, six hundred forty-nine".