21020561644 has 12 divisors (see below), whose sum is σ = 36790789168. Its totient is φ = 10508907600.

The previous prime is 21020561641. The next prime is 21020561647. The reversal of 21020561644 is 44616502012.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21020561641) and next prime (21020561647).

It is a super-3 number, since 3×21020561644³ (a number of 32 digits) contains 333 as substring.

It is not an unprimeable number, because it can be changed into a prime (21020561641) 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 3 ways as a sum of consecutive naturals, for example, 308472 + ... + 370399.

Almost surely, 2^21020561644 is an apocalyptic number.

It is an amenable number.

21020561644 is a deficient number, since it is larger than the sum of its proper divisors (15770227524).

21020561644 is a wasteful number, since it uses less digits than its factorization.

21020561644 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 686616 (or 686614 counting only the distinct ones).

The product of its (nonzero) digits is 11520, while the sum is 31.

The spelling of 21020561644 in words is "twenty-one billion, twenty million, five hundred sixty-one thousand, six hundred forty-four".