6991981 has 8 divisors (see below), whose sum is σ = 7793280. Its totient is φ = 6234048.

The previous prime is 6991979. The next prime is 6991991. The reversal of 6991981 is 1891996.

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 6991981 - 2¹ = 6991979 is a prime.

It is a super-2 number, since 2×6991981² = 97775596608722, which contains 22 as substring.

It is a Duffinian number.

6991981 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6991951) 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, 10501 + ... + 11146.

It is an arithmetic number, because the mean of its divisors is an integer number (974160).

Almost surely, 2^6991981 is an apocalyptic number.

It is an amenable number.

6991981 is a deficient number, since it is larger than the sum of its proper divisors (801299).

6991981 is a wasteful number, since it uses less digits than its factorization.

6991981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21683.

The product of its digits is 34992, while the sum is 43.

The square root of 6991981 is about 2644.2354282476. The cubic root of 6991981 is about 191.2200437225.

The spelling of 6991981 in words is "six million, nine hundred ninety-one thousand, nine hundred eighty-one".