7921578771561 has 72 divisors (see below), whose sum is σ = 13305840344640. Its totient is φ = 4177946957184.

The previous prime is 7921578771499. The next prime is 7921578771563. The reversal of 7921578771561 is 1651778751297.

It is not a de Polignac number, because 7921578771561 - 2⁶ = 7921578771497 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 7921578771492 and 7921578771501.

It is not an unprimeable number, because it can be changed into a prime (7921578771563) by changing a digit.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 429600780 + ... + 429619218.

It is an arithmetic number, because the mean of its divisors is an integer number (184803338120).

Almost surely, 2^{7921578771561} is an apocalyptic number.

It is an amenable number.

7921578771561 is a deficient number, since it is larger than the sum of its proper divisors (5384261573079).

7921578771561 is a wasteful number, since it uses less digits than its factorization.

7921578771561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35775 (or 35755 counting only the distinct ones).

The product of its digits is 51861600, while the sum is 66.

The spelling of 7921578771561 in words is "seven trillion, nine hundred twenty-one billion, five hundred seventy-eight million, seven hundred seventy-one thousand, five hundred sixty-one".