21887461781 has 4 divisors (see below), whose sum is σ = 22300432812. Its totient is φ = 21474490752.

The previous prime is 21887461741. The next prime is 21887461807. The reversal of 21887461781 is 18716478812.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 5798822500 + 16088639281 = 76150^2 + 126841^2 .

It is a cyclic number.

It is not a de Polignac number, because 21887461781 - 2¹⁴ = 21887445397 is a prime.

It is a super-2 number, since 2×21887461781² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (53), and also a Moran number because the ratio is a prime number: 412970977 = 21887461781 / (2 + 1 + 8 + 8 + 7 + 4 + 6 + 1 + 7 + 8 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21887461721) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 206485436 + ... + 206485541.

It is an arithmetic number, because the mean of its divisors is an integer number (5575108203).

Almost surely, 2^21887461781 is an apocalyptic number.

It is an amenable number.

21887461781 is a deficient number, since it is larger than the sum of its proper divisors (412971031).

21887461781 is an equidigital number, since it uses as much as digits as its factorization.

21887461781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 412971030.

The product of its digits is 1204224, while the sum is 53.

The spelling of 21887461781 in words is "twenty-one billion, eight hundred eighty-seven million, four hundred sixty-one thousand, seven hundred eighty-one".