21155663 has 2 divisors, whose sum is σ = 21155664. Its totient is φ = 21155662.

The previous prime is 21155627. The next prime is 21155669. The reversal of 21155663 is 36655112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21155663 - 2¹⁶ = 21090127 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21155669) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10577831 + 10577832.

It is an arithmetic number, because the mean of its divisors is an integer number (10577832).

Almost surely, 2^21155663 is an apocalyptic number.

21155663 is a deficient number, since it is larger than the sum of its proper divisors (1).

21155663 is an equidigital number, since it uses as much as digits as its factorization.

21155663 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5400, while the sum is 29.

The square root of 21155663 is about 4599.5285627986. The cubic root of 21155663 is about 276.5724265730.

The spelling of 21155663 in words is "twenty-one million, one hundred fifty-five thousand, six hundred sixty-three".