1287978991 has 16 divisors (see below), whose sum is σ = 1427049568. Its totient is φ = 1154736000.

The previous prime is 1287978971. The next prime is 1287979003. The reversal of 1287978991 is 1998797821.

It is a cyclic number.

It is not a de Polignac number, because 1287978991 - 2¹⁷ = 1287847919 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1287978941) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 315916 + ... + 319966.

It is an arithmetic number, because the mean of its divisors is an integer number (89190598).

Almost surely, 2^1287978991 is an apocalyptic number.

1287978991 is a deficient number, since it is larger than the sum of its proper divisors (139070577).

1287978991 is a wasteful number, since it uses less digits than its factorization.

1287978991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4762.

The product of its digits is 4572288, while the sum is 61.

The square root of 1287978991 is about 35888.4241922099. The cubic root of 1287978991 is about 1088.0184493407.

The spelling of 1287978991 in words is "one billion, two hundred eighty-seven million, nine hundred seventy-eight thousand, nine hundred ninety-one".