21144040020 has 72 divisors (see below), whose sum is σ = 67909691304. Its totient is φ = 5306738688.

The previous prime is 21144040019. The next prime is 21144040061. The reversal of 21144040020 is 2004044112.

It can be written as a sum of positive squares in 4 ways, for example, as 4201373124 + 16942666896 = 64818^2 + 130164^2 .

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21144039975 and 21144040002.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3451849 + ... + 3457968.

It is an arithmetic number, because the mean of its divisors is an integer number (943190157).

Almost surely, 2^21144040020 is an apocalyptic number.

21144040020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21144040020 is an abundant number, since it is smaller than the sum of its proper divisors (46765651284).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21144040020 is a wasteful number, since it uses less digits than its factorization.

21144040020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6909849 (or 6909844 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 18.

Adding to 21144040020 its reverse (2004044112), we get a palindrome (23148084132).

The spelling of 21144040020 in words is "twenty-one billion, one hundred forty-four million, forty thousand, twenty".