421991 has 8 divisors (see below), whose sum is σ = 453024. Its totient is φ = 391680.

The previous prime is 421987. The next prime is 421997. The reversal of 421991 is 199124.

421991 = T₃₄ + T₃₅ + ... + T₁₃₆.

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

It is not a de Polignac number, because 421991 - 2² = 421987 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a zygodrome in base 2.

It is a self number, because there is not a number n which added to its sum of digits gives 421991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (421997) 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, 1631 + ... + 1871.

It is an arithmetic number, because the mean of its divisors is an integer number (56628).

2⁴²¹⁹⁹¹ is an apocalyptic number.

421991 is a deficient number, since it is larger than the sum of its proper divisors (31033).

421991 is a wasteful number, since it uses less digits than its factorization.

421991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 361.

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

The square root of 421991 is about 649.6083435425. The cubic root of 421991 is about 75.0068734441.

The spelling of 421991 in words is "four hundred twenty-one thousand, nine hundred ninety-one".