21021715 has 16 divisors (see below), whose sum is σ = 29637216. Its totient is φ = 14112000.

The previous prime is 21021713. The next prime is 21021739. The reversal of 21021715 is 51712012.

It is not a de Polignac number, because 21021715 - 2¹ = 21021713 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21021692 and 21021701.

It is not an unprimeable number, because it can be changed into a prime (21021713) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 13986 + ... + 15415.

It is an arithmetic number, because the mean of its divisors is an integer number (1852326).

Almost surely, 2^21021715 is an apocalyptic number.

21021715 is a deficient number, since it is larger than the sum of its proper divisors (8615501).

21021715 is a wasteful number, since it uses less digits than its factorization.

21021715 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29430.

The product of its (nonzero) digits is 140, while the sum is 19.

The square root of 21021715 is about 4584.9443835231. The cubic root of 21021715 is about 275.9874801784.

Adding to 21021715 its reverse (51712012), we get a palindrome (72733727).

It can be divided in two parts, 21021 and 715, that added together give a triangular number (21736 = T₂₀₈).

The spelling of 21021715 in words is "twenty-one million, twenty-one thousand, seven hundred fifteen".