1391878981 has 4 divisors (see below), whose sum is σ = 1392749964. Its totient is φ = 1391008000.

The previous prime is 1391878973. The next prime is 1391878993. The reversal of 1391878981 is 1898781931.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 828576225 + 563302756 = 28785^2 + 23734^2 .

It is a cyclic number.

It is not a de Polignac number, because 1391878981 - 2³ = 1391878973 is a prime.

It is a super-2 number, since 2×1391878981² = 3874654195499196722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1391878181) 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, 433090 + ... + 436291.

It is an arithmetic number, because the mean of its divisors is an integer number (348187491).

Almost surely, 2^1391878981 is an apocalyptic number.

It is an amenable number.

1391878981 is a deficient number, since it is larger than the sum of its proper divisors (870983).

1391878981 is an equidigital number, since it uses as much as digits as its factorization.

1391878981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 870982.

The product of its digits is 870912, while the sum is 55.

The square root of 1391878981 is about 37307.8943522681. The cubic root of 1391878981 is about 1116.5216760537.

The spelling of 1391878981 in words is "one billion, three hundred ninety-one million, eight hundred seventy-eight thousand, nine hundred eighty-one".