21556263169921 has 2 divisors, whose sum is σ = 21556263169922. Its totient is φ = 21556263169920.

The previous prime is 21556263169897. The next prime is 21556263169933. The reversal of 21556263169921 is 12996136265512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21089118259521 + 467144910400 = 4592289^2 + 683480^2 .

It is a cyclic number.

It is not a de Polignac number, because 21556263169921 - 2¹³ = 21556263161729 is a prime.

It is not a weakly prime, because it can be changed into another prime (21556263169421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10778131584960 + 10778131584961.

It is an arithmetic number, because the mean of its divisors is an integer number (10778131584961).

Almost surely, 2^{21556263169921} is an apocalyptic number.

It is an amenable number.

21556263169921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21556263169921 is an equidigital number, since it uses as much as digits as its factorization.

21556263169921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10497600, while the sum is 58.

The spelling of 21556263169921 in words is "twenty-one trillion, five hundred fifty-six billion, two hundred sixty-three million, one hundred sixty-nine thousand, nine hundred twenty-one".