21618263203781 has 4 divisors (see below), whose sum is σ = 21618272545452. Its totient is φ = 21618253862112.

The previous prime is 21618263203777. The next prime is 21618263203841. The reversal of 21618263203781 is 18730236281612.

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 can be written as a sum of positive squares in 2 ways, for example, as 4116674623681 + 17501588580100 = 2028959^2 + 4183490^2 .

It is a cyclic number.

It is not a de Polignac number, because 21618263203781 - 2² = 21618263203777 is a prime.

It is a super-2 number, since 2×21618263203781² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21618263203741) 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, 1667225 + ... + 6783521.

It is an arithmetic number, because the mean of its divisors is an integer number (5404568136363).

Almost surely, 2^{21618263203781} is an apocalyptic number.

It is an amenable number.

21618263203781 is a deficient number, since it is larger than the sum of its proper divisors (9341671).

21618263203781 is an equidigital number, since it uses as much as digits as its factorization.

21618263203781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9341670.

The product of its (nonzero) digits is 1161216, while the sum is 50.

The spelling of 21618263203781 in words is "twenty-one trillion, six hundred eighteen billion, two hundred sixty-three million, two hundred three thousand, seven hundred eighty-one".