21931686649 has 2 divisors, whose sum is σ = 21931686650. Its totient is φ = 21931686648.

The previous prime is 21931686617. The next prime is 21931686661. The reversal of 21931686649 is 94668613912.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11439372025 + 10492314624 = 106955^2 + 102432^2 .

It is a cyclic number.

It is not a de Polignac number, because 21931686649 - 2⁵ = 21931686617 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21931686649.

It is not a weakly prime, because it can be changed into another prime (21931686449) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10965843324 + 10965843325.

It is an arithmetic number, because the mean of its divisors is an integer number (10965843325).

Almost surely, 2^21931686649 is an apocalyptic number.

It is an amenable number.

21931686649 is a deficient number, since it is larger than the sum of its proper divisors (1).

21931686649 is an equidigital number, since it uses as much as digits as its factorization.

21931686649 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3359232, while the sum is 55.

The spelling of 21931686649 in words is "twenty-one billion, nine hundred thirty-one million, six hundred eighty-six thousand, six hundred forty-nine".