1971991 has 8 divisors (see below), whose sum is σ = 2372480. Its totient is φ = 1601208.

The previous prime is 1971967. The next prime is 1972007. The reversal of 1971991 is 1991791.

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

It is not a de Polignac number, because 1971991 - 2⁹ = 1971479 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 1971991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1971901) 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, 7281 + ... + 7546.

It is an arithmetic number, because the mean of its divisors is an integer number (296560).

2^1971991 is an apocalyptic number.

1971991 is a deficient number, since it is larger than the sum of its proper divisors (400489).

1971991 is a wasteful number, since it uses less digits than its factorization.

1971991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14853.

The product of its digits is 5103, while the sum is 37.

The square root of 1971991 is about 1404.2759700287. The cubic root of 1971991 is about 125.4011856895.

It can be divided in two parts, 19 and 71991, that added together give a triangular number (72010 = T₃₇₉).

The spelling of 1971991 in words is "one million, nine hundred seventy-one thousand, nine hundred ninety-one".