21051691526809 has 2 divisors, whose sum is σ = 21051691526810. Its totient is φ = 21051691526808.

The previous prime is 21051691526731. The next prime is 21051691526819. The reversal of 21051691526809 is 90862519615012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17408479488409 + 3643212038400 = 4172347^2 + 1908720^2 .

It is a cyclic number.

It is not a de Polignac number, because 21051691526809 - 2¹⁹ = 21051691002521 is a prime.

It is a super-2 number, since 2×21051691526809² (a number of 27 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21051691526809.

It is not a weakly prime, because it can be changed into another prime (21051691526819) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10525845763404 + 10525845763405.

It is an arithmetic number, because the mean of its divisors is an integer number (10525845763405).

Almost surely, 2^{21051691526809} is an apocalyptic number.

It is an amenable number.

21051691526809 is a deficient number, since it is larger than the sum of its proper divisors (1).

21051691526809 is an equidigital number, since it uses as much as digits as its factorization.

21051691526809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2332800, while the sum is 55.

The spelling of 21051691526809 in words is "twenty-one trillion, fifty-one billion, six hundred ninety-one million, five hundred twenty-six thousand, eight hundred nine".