78811721 has 2 divisors, whose sum is σ = 78811722. Its totient is φ = 78811720.

The previous prime is 78811709. The next prime is 78811723. The reversal of 78811721 is 12711887.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 59845696 + 18966025 = 7736^2 + 4355^2 .

It is a cyclic number.

It is not a de Polignac number, because 78811721 - 2⁶ = 78811657 is a prime.

It is a super-2 number, since 2×78811721² = 12422574733963682, which contains 22 as substring.

Together with 78811723, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (78811723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39405860 + 39405861.

It is an arithmetic number, because the mean of its divisors is an integer number (39405861).

Almost surely, 2^78811721 is an apocalyptic number.

It is an amenable number.

78811721 is a deficient number, since it is larger than the sum of its proper divisors (1).

78811721 is an equidigital number, since it uses as much as digits as its factorization.

78811721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6272, while the sum is 35.

The square root of 78811721 is about 8877.5965779033. The cubic root of 78811721 is about 428.7428959545.

The spelling of 78811721 in words is "seventy-eight million, eight hundred eleven thousand, seven hundred twenty-one".