6661721 has 8 divisors (see below), whose sum is σ = 7445088. Its totient is φ = 5908000.

The previous prime is 6661709. The next prime is 6661727. The reversal of 6661721 is 1271666.

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 6661721 - 2¹⁸ = 6399577 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6661727) 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, 6935 + ... + 7836.

It is an arithmetic number, because the mean of its divisors is an integer number (930636).

Almost surely, 2^6661721 is an apocalyptic number.

It is an amenable number.

6661721 is a deficient number, since it is larger than the sum of its proper divisors (783367).

6661721 is a wasteful number, since it uses less digits than its factorization.

6661721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14823.

The product of its digits is 3024, while the sum is 29.

The square root of 6661721 is about 2581.0309955520. The cubic root of 6661721 is about 188.1606537576.

The spelling of 6661721 in words is "six million, six hundred sixty-one thousand, seven hundred twenty-one".