1391864921 has 2 divisors, whose sum is σ = 1391864922. Its totient is φ = 1391864920.

The previous prime is 1391864917. The next prime is 1391865011. The reversal of 1391864921 is 1294681931.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1051056400 + 340808521 = 32420^2 + 18461^2 .

It is an emirp because it is prime and its reverse (1294681931) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1391864921 - 2² = 1391864917 is a prime.

It is not a weakly prime, because it can be changed into another prime (1391861921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 695932460 + 695932461.

It is an arithmetic number, because the mean of its divisors is an integer number (695932461).

Almost surely, 2^1391864921 is an apocalyptic number.

It is an amenable number.

1391864921 is a deficient number, since it is larger than the sum of its proper divisors (1).

1391864921 is an equidigital number, since it uses as much as digits as its factorization.

1391864921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 93312, while the sum is 44.

The square root of 1391864921 is about 37307.7059198231. The cubic root of 1391864921 is about 1116.5179165440.

The spelling of 1391864921 in words is "one billion, three hundred ninety-one million, eight hundred sixty-four thousand, nine hundred twenty-one".