1991717890 has 16 divisors (see below), whose sum is σ = 3740966208. Its totient is φ = 762048496.

The previous prime is 1991717839. The next prime is 1991717933. The reversal of 1991717890 is 987171991.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4329592 + ... + 4330051.

It is an arithmetic number, because the mean of its divisors is an integer number (233810388).

Almost surely, 2^1991717890 is an apocalyptic number.

1991717890 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

1991717890 is a deficient number, since it is larger than the sum of its proper divisors (1749248318).

1991717890 is a wasteful number, since it uses less digits than its factorization.

1991717890 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8659673.

The product of its (nonzero) digits is 285768, while the sum is 52.

The square root of 1991717890 is about 44628.6666840944. Note that the first 4 decimals coincide. The cubic root of 1991717890 is about 1258.1795096190.

The spelling of 1991717890 in words is "one billion, nine hundred ninety-one million, seven hundred seventeen thousand, eight hundred ninety".