21138542881 has 3 divisors (see below), whose sum is σ = 21138688273. Its totient is φ = 21138397490.

The previous prime is 21138542861. The next prime is 21138542923. The reversal of 21138542881 is 18824583112.

The square root of 21138542881 is 145391.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is not a de Polignac number, because 21138542881 - 2⁷ = 21138542753 is a prime.

It is a super-2 number, since 2×21138542881² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21138542861) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 72696 + ... + 218086.

Almost surely, 2^21138542881 is an apocalyptic number.

21138542881 is the 145391-st square number.

21138542881 is the 72696-th centered octagonal number.

It is an amenable number.

21138542881 is a deficient number, since it is larger than the sum of its proper divisors (145392).

21138542881 is an frugal number, since it uses more digits than its factorization.

21138542881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 290782 (or 145391 counting only the distinct ones).

The product of its digits is 122880, while the sum is 43.

The spelling of 21138542881 in words is "twenty-one billion, one hundred thirty-eight million, five hundred forty-two thousand, eight hundred eighty-one".