21556678865503 has 4 divisors (see below), whose sum is σ = 21910067043688. Its totient is φ = 21203290687320.

The previous prime is 21556678865497. The next prime is 21556678865521. The reversal of 21556678865503 is 30556887665512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21556678865503 - 2⁴¹ = 19357655609951 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21556678875503) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 176694089001 + ... + 176694089122.

It is an arithmetic number, because the mean of its divisors is an integer number (5477516760922).

Almost surely, 2^{21556678865503} is an apocalyptic number.

21556678865503 is a deficient number, since it is larger than the sum of its proper divisors (353388178185).

21556678865503 is an equidigital number, since it uses as much as digits as its factorization.

21556678865503 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 353388178184.

The product of its (nonzero) digits is 362880000, while the sum is 67.

The spelling of 21556678865503 in words is "twenty-one trillion, five hundred fifty-six billion, six hundred seventy-eight million, eight hundred sixty-five thousand, five hundred three".