8400721 has 8 divisors (see below), whose sum is σ = 9910784. Its totient is φ = 6968160.

The previous prime is 8400713. The next prime is 8400731. The reversal of 8400721 is 1270048.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 8400721 - 2³ = 8400713 is a prime.

It is a super-2 number, since 2×8400721² = 141144226639682, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 8400692 and 8400701.

It is not an unprimeable number, because it can be changed into a prime (8400701) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 19140 + ... + 19573.

It is an arithmetic number, because the mean of its divisors is an integer number (1238848).

Almost surely, 2^8400721 is an apocalyptic number.

It is an amenable number.

8400721 is a deficient number, since it is larger than the sum of its proper divisors (1510063).

8400721 is a wasteful number, since it uses less digits than its factorization.

8400721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 38751.

The product of its (nonzero) digits is 448, while the sum is 22.

The square root of 8400721 is about 2898.3997308860. The cubic root of 8400721 is about 203.2850872424.

Adding to 8400721 its reverse (1270048), we get a palindrome (9670769).

The spelling of 8400721 in words is "eight million, four hundred thousand, seven hundred twenty-one".