78420721517 has 4 divisors (see below), whose sum is σ = 78422845920. Its totient is φ = 78418597116.

The previous prime is 78420721493. The next prime is 78420721531. The reversal of 78420721517 is 71512702487.

It is a happy number.

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 an emirpimes, since its reverse is a distinct semiprime: 71512702487 = 4057 ⋅17626991.

It is a cyclic number.

It is not a de Polignac number, because 78420721517 - 2⁶ = 78420721453 is a prime.

It is a super-2 number, since 2×78420721517² (a number of 23 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (78420721117) 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, 1005833 + ... + 1080990.

It is an arithmetic number, because the mean of its divisors is an integer number (19605711480).

Almost surely, 2^78420721517 is an apocalyptic number.

It is an amenable number.

78420721517 is a deficient number, since it is larger than the sum of its proper divisors (2124403).

78420721517 is a wasteful number, since it uses less digits than its factorization.

78420721517 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2124402.

The product of its (nonzero) digits is 219520, while the sum is 44.

The spelling of 78420721517 in words is "seventy-eight billion, four hundred twenty million, seven hundred twenty-one thousand, five hundred seventeen".