40021991 has 4 divisors (see below), whose sum is σ = 40034952. Its totient is φ = 40009032.

The previous prime is 40021973. The next prime is 40021997. The reversal of 40021991 is 19912004.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-40021991 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 40021991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (40021997) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1136 + ... + 9018.

It is an arithmetic number, because the mean of its divisors is an integer number (10008738).

Almost surely, 2^40021991 is an apocalyptic number.

40021991 is a deficient number, since it is larger than the sum of its proper divisors (12961).

40021991 is an equidigital number, since it uses as much as digits as its factorization.

40021991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12960.

The product of its (nonzero) digits is 648, while the sum is 26.

The square root of 40021991 is about 6326.2936226514. The cubic root of 40021991 is about 342.0578513218.

Adding to 40021991 its reverse (19912004), we get a palindrome (59933995).

The spelling of 40021991 in words is "forty million, twenty-one thousand, nine hundred ninety-one".