21356257661655 has 24 divisors (see below), whose sum is σ = 39748789771632. Its totient is φ = 9762860644992.

The previous prime is 21356257661639. The next prime is 21356257661659. The reversal of 21356257661655 is 55616675265312.

It is not a de Polignac number, because 21356257661655 - 2⁴ = 21356257661639 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21356257661659) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 14528065702 + ... + 14528067171.

It is an arithmetic number, because the mean of its divisors is an integer number (1656199573818).

Almost surely, 2^{21356257661655} is an apocalyptic number.

21356257661655 is a deficient number, since it is larger than the sum of its proper divisors (18392532109977).

21356257661655 is a wasteful number, since it uses less digits than its factorization.

21356257661655 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29056132895 (or 29056132888 counting only the distinct ones).

The product of its digits is 68040000, while the sum is 60.

The spelling of 21356257661655 in words is "twenty-one trillion, three hundred fifty-six billion, two hundred fifty-seven million, six hundred sixty-one thousand, six hundred fifty-five".