18978961 has 4 divisors (see below), whose sum is σ = 19003572. Its totient is φ = 18954352.

The previous prime is 18978959. The next prime is 18978989. The reversal of 18978961 is 16987981.

18978961 = 3080² + 3081².

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 9486400 + 9492561 = 3080^2 + 3081^2 .

It is a cyclic number.

It is not a de Polignac number, because 18978961 - 2¹ = 18978959 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18978901) 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, 11110 + ... + 12703.

It is an arithmetic number, because the mean of its divisors is an integer number (4750893).

Almost surely, 2^18978961 is an apocalyptic number.

18978961 is the 3081-st centered square number.

It is an amenable number.

18978961 is a deficient number, since it is larger than the sum of its proper divisors (24611).

18978961 is an equidigital number, since it uses as much as digits as its factorization.

18978961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24610.

The product of its digits is 217728, while the sum is 49.

The square root of 18978961 is about 4356.4849362760. The cubic root of 18978961 is about 266.7416363866.

The spelling of 18978961 in words is "eighteen million, nine hundred seventy-eight thousand, nine hundred sixty-one".