1561673320778 has 4 divisors (see below), whose sum is σ = 2342509981170. Its totient is φ = 780836660388.

The previous prime is 1561673320771. The next prime is 1561673320783. The reversal of 1561673320778 is 8770233761651.

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

It can be written as a sum of positive squares in only one way, i.e., 1086383036209 + 475290284569 = 1042297^2 + 689413^2 .

It is not an unprimeable number, because it can be changed into a prime (1561673320771) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 390418330193 + ... + 390418330196.

Almost surely, 2^{1561673320778} is an apocalyptic number.

1561673320778 is a deficient number, since it is larger than the sum of its proper divisors (780836660392).

1561673320778 is an equidigital number, since it uses as much as digits as its factorization.

1561673320778 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 780836660391.

The product of its (nonzero) digits is 8890560, while the sum is 56.

The spelling of 1561673320778 in words is "one trillion, five hundred sixty-one billion, six hundred seventy-three million, three hundred twenty thousand, seven hundred seventy-eight".