6720421 has 6 divisors (see below), whose sum is σ = 6908370. Its totient is φ = 6537456.

The previous prime is 6720409. The next prime is 6720437. The reversal of 6720421 is 1240276.

6720421 = T₂₉₁ + T₂₉₂ + ... + T₄₀₁.

It can be written as a sum of positive squares in 3 ways, for example, as 5827396 + 893025 = 2414^2 + 945^2 .

It is a de Polignac number, because none of the positive numbers 2^k-6720421 is a prime.

It is a Duffinian number.

6720421 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 6720392 and 6720401.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6720481) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1086 + ... + 3823.

It is an arithmetic number, because the mean of its divisors is an integer number (1151395).

Almost surely, 2^6720421 is an apocalyptic number.

It is an amenable number.

6720421 is a deficient number, since it is larger than the sum of its proper divisors (187949).

6720421 is an equidigital number, since it uses as much as digits as its factorization.

6720421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4983 (or 4946 counting only the distinct ones).

The product of its (nonzero) digits is 672, while the sum is 22.

The square root of 6720421 is about 2592.3774802293. The cubic root of 6720421 is about 188.7116999025.

Adding to 6720421 its reverse (1240276), we get a palindrome (7960697).

The spelling of 6720421 in words is "six million, seven hundred twenty thousand, four hundred twenty-one".