21155055421 has 2 divisors, whose sum is σ = 21155055422. Its totient is φ = 21155055420.

The previous prime is 21155055331. The next prime is 21155055451. The reversal of 21155055421 is 12455055112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19491231321 + 1663824100 = 139611^2 + 40790^2 .

It is a cyclic number.

It is not a de Polignac number, because 21155055421 - 2¹¹ = 21155053373 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21155055451) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10577527710 + 10577527711.

It is an arithmetic number, because the mean of its divisors is an integer number (10577527711).

Almost surely, 2^21155055421 is an apocalyptic number.

It is an amenable number.

21155055421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21155055421 is an equidigital number, since it uses as much as digits as its factorization.

21155055421 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 10000, while the sum is 31.

The spelling of 21155055421 in words is "twenty-one billion, one hundred fifty-five million, fifty-five thousand, four hundred twenty-one".