78621017557 has 4 divisors (see below), whose sum is σ = 78621642496. Its totient is φ = 78620392620.

The previous prime is 78621017539. The next prime is 78621017569. The reversal of 78621017557 is 75571012687.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 78621017557 - 2¹¹ = 78621015509 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 78621017557.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (78621017537) 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, 50613 + ... + 399754.

It is an arithmetic number, because the mean of its divisors is an integer number (19655410624).

Almost surely, 2^78621017557 is an apocalyptic number.

It is an amenable number.

78621017557 is a deficient number, since it is larger than the sum of its proper divisors (624939).

78621017557 is a wasteful number, since it uses less digits than its factorization.

78621017557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 624938.

The product of its (nonzero) digits is 823200, while the sum is 49.

The spelling of 78621017557 in words is "seventy-eight billion, six hundred twenty-one million, seventeen thousand, five hundred fifty-seven".