21257381281 has 8 divisors (see below), whose sum is σ = 22651180200. Its totient is φ = 19879511808.

The previous prime is 21257381273. The next prime is 21257381291. The reversal of 21257381281 is 18218375212.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 538657681 + 20718723600 = 23209^2 + 143940^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21257381281 - 2³ = 21257381273 is a prime.

It is a super-2 number, since 2×21257381281² (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 (21257381231) 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 7 ways as a sum of consecutive naturals, for example, 3979606 + ... + 3984943.

It is an arithmetic number, because the mean of its divisors is an integer number (2831397525).

Almost surely, 2^21257381281 is an apocalyptic number.

It is an amenable number.

21257381281 is a deficient number, since it is larger than the sum of its proper divisors (1393798919).

21257381281 is a wasteful number, since it uses less digits than its factorization.

21257381281 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7964723.

The product of its digits is 53760, while the sum is 40.

The spelling of 21257381281 in words is "twenty-one billion, two hundred fifty-seven million, three hundred eighty-one thousand, two hundred eighty-one".