1921978 has 4 divisors (see below), whose sum is σ = 2882970. Its totient is φ = 960988.

The previous prime is 1921967. The next prime is 1921981. The reversal of 1921978 is 8791291.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 8791291 = 71 ⋅123821.

It can be written as a sum of positive squares in only one way, i.e., 1734489 + 187489 = 1317^2 + 433^2 .

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 480493 + ... + 480496.

2^1921978 is an apocalyptic number.

1921978 is a deficient number, since it is larger than the sum of its proper divisors (960992).

1921978 is an equidigital number, since it uses as much as digits as its factorization.

1921978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 960991.

The product of its digits is 9072, while the sum is 37.

The square root of 1921978 is about 1386.3542115924. The cubic root of 1921978 is about 124.3319668806.

The spelling of 1921978 in words is "one million, nine hundred twenty-one thousand, nine hundred seventy-eight".