7728400742921 has 4 divisors (see below), whose sum is σ = 7728419222292. Its totient is φ = 7728382263552.

The previous prime is 7728400742879. The next prime is 7728400742927. The reversal of 7728400742921 is 1292470048277.

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 716073056521 + 7012327686400 = 846211^2 + 2648080^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-7728400742921 is a prime.

It is a super-2 number, since 2×7728400742921² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (7728400742927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8597480 + ... + 9453753.

It is an arithmetic number, because the mean of its divisors is an integer number (1932104805573).

Almost surely, 2^{7728400742921} is an apocalyptic number.

It is an amenable number.

7728400742921 is a deficient number, since it is larger than the sum of its proper divisors (18479371).

7728400742921 is a wasteful number, since it uses less digits than its factorization.

7728400742921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18479370.

The product of its (nonzero) digits is 3161088, while the sum is 53.

The spelling of 7728400742921 in words is "seven trillion, seven hundred twenty-eight billion, four hundred million, seven hundred forty-two thousand, nine hundred twenty-one".