21645703861 has 2 divisors, whose sum is σ = 21645703862. Its totient is φ = 21645703860.

The previous prime is 21645703847. The next prime is 21645703889. The reversal of 21645703861 is 16830754612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21628114225 + 17589636 = 147065^2 + 4194^2 .

It is a cyclic number.

It is not a de Polignac number, because 21645703861 - 2²¹ = 21643606709 is a prime.

It is a super-2 number, since 2×21645703861² (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 (21645703561) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10822851930 + 10822851931.

It is an arithmetic number, because the mean of its divisors is an integer number (10822851931).

Almost surely, 2^21645703861 is an apocalyptic number.

It is an amenable number.

21645703861 is a deficient number, since it is larger than the sum of its proper divisors (1).

21645703861 is an equidigital number, since it uses as much as digits as its factorization.

21645703861 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 241920, while the sum is 43.

The spelling of 21645703861 in words is "twenty-one billion, six hundred forty-five million, seven hundred three thousand, eight hundred sixty-one".