78142721 has 2 divisors, whose sum is σ = 78142722. Its totient is φ = 78142720.

The previous prime is 78142697. The next prime is 78142747. The reversal of 78142721 is 12724187.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 73017025 + 5125696 = 8545^2 + 2264^2 .

It is a cyclic number.

It is not a de Polignac number, because 78142721 - 2⁶ = 78142657 is a prime.

It is a super-2 number, since 2×78142721² = 12212569690567682, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (78142021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39071360 + 39071361.

It is an arithmetic number, because the mean of its divisors is an integer number (39071361).

Almost surely, 2^78142721 is an apocalyptic number.

It is an amenable number.

78142721 is a deficient number, since it is larger than the sum of its proper divisors (1).

78142721 is an equidigital number, since it uses as much as digits as its factorization.

78142721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6272, while the sum is 32.

The square root of 78142721 is about 8839.8371591336. The cubic root of 78142721 is about 427.5263068749.

The spelling of 78142721 in words is "seventy-eight million, one hundred forty-two thousand, seven hundred twenty-one".