7821211978 has 4 divisors (see below), whose sum is σ = 11731817970. Its totient is φ = 3910605988.

The previous prime is 7821211949. The next prime is 7821212011. The reversal of 7821211978 is 8791121287.

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., 7236394489 + 584817489 = 85067^2 + 24183^2 .

It is a super-2 number, since 2×7821211978² (a number of 21 digits) contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1955302993 + ... + 1955302996.

Almost surely, 2^7821211978 is an apocalyptic number.

7821211978 is a deficient number, since it is larger than the sum of its proper divisors (3910605992).

7821211978 is a wasteful number, since it uses less digits than its factorization.

7821211978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3910605991.

The product of its digits is 112896, while the sum is 46.

The square root of 7821211978 is about 88437.6163066373. The cubic root of 7821211978 is about 1984.9886091300.

The spelling of 7821211978 in words is "seven billion, eight hundred twenty-one million, two hundred eleven thousand, nine hundred seventy-eight".