21540332381 has 2 divisors, whose sum is σ = 21540332382. Its totient is φ = 21540332380.

The previous prime is 21540332377. The next prime is 21540332389. The reversal of 21540332381 is 18323304512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21394912900 + 145419481 = 146270^2 + 12059^2 .

It is a cyclic number.

It is not a de Polignac number, because 21540332381 - 2² = 21540332377 is a prime.

It is a super-2 number, since 2×21540332381² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21540332389) 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, 10770166190 + 10770166191.

It is an arithmetic number, because the mean of its divisors is an integer number (10770166191).

Almost surely, 2^21540332381 is an apocalyptic number.

It is an amenable number.

21540332381 is a deficient number, since it is larger than the sum of its proper divisors (1).

21540332381 is an equidigital number, since it uses as much as digits as its factorization.

21540332381 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 17280, while the sum is 32.

Adding to 21540332381 its reverse (18323304512), we get a palindrome (39863636893).

The spelling of 21540332381 in words is "twenty-one billion, five hundred forty million, three hundred thirty-two thousand, three hundred eighty-one".