21512720 has 20 divisors (see below), whose sum is σ = 50017260. Its totient is φ = 8605056.

The previous prime is 21512719. The next prime is 21512747. The reversal of 21512720 is 2721512.

It can be written as a sum of positive squares in 2 ways, for example, as 2572816 + 18939904 = 1604^2 + 4352^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a junction number, because it is equal to n+sod(n) for n = 21512692 and 21512701.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 134375 + ... + 134534.

It is an arithmetic number, because the mean of its divisors is an integer number (2500863).

Almost surely, 2^21512720 is an apocalyptic number.

21512720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21512720 is an abundant number, since it is smaller than the sum of its proper divisors (28504540).

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

21512720 is a wasteful number, since it uses less digits than its factorization.

21512720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 268922 (or 268916 counting only the distinct ones).

The product of its (nonzero) digits is 280, while the sum is 20.

The square root of 21512720 is about 4638.1806778089. The cubic root of 21512720 is about 278.1197144979.

It can be divided in two parts, 21 and 512720, that multiplied together give a triangular number (10767120 = T₄₆₄₀).

The spelling of 21512720 in words is "twenty-one million, five hundred twelve thousand, seven hundred twenty".