21055543657 has 2 divisors, whose sum is σ = 21055543658. Its totient is φ = 21055543656.

The previous prime is 21055543627. The next prime is 21055543669. The reversal of 21055543657 is 75634555012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19348531801 + 1707011856 = 139099^2 + 41316^2 .

It is a cyclic number.

It is not a de Polignac number, because 21055543657 - 2¹⁹ = 21055019369 is a prime.

It is not a weakly prime, because it can be changed into another prime (21055543627) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10527771828 + 10527771829.

It is an arithmetic number, because the mean of its divisors is an integer number (10527771829).

Almost surely, 2^21055543657 is an apocalyptic number.

It is an amenable number.

21055543657 is a deficient number, since it is larger than the sum of its proper divisors (1).

21055543657 is an equidigital number, since it uses as much as digits as its factorization.

21055543657 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 630000, while the sum is 43.

The spelling of 21055543657 in words is "twenty-one billion, fifty-five million, five hundred forty-three thousand, six hundred fifty-seven".