78921581 has 2 divisors, whose sum is σ = 78921582. Its totient is φ = 78921580.

The previous prime is 78921539. The next prime is 78921589. The reversal of 78921581 is 18512987.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 75099556 + 3822025 = 8666^2 + 1955^2 .

It is a cyclic number.

It is not a de Polignac number, because 78921581 - 2¹⁸ = 78659437 is a prime.

It is a super-2 number, since 2×78921581² = 12457231895079122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78921589) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39460790 + 39460791.

It is an arithmetic number, because the mean of its divisors is an integer number (39460791).

Almost surely, 2^78921581 is an apocalyptic number.

It is an amenable number.

78921581 is a deficient number, since it is larger than the sum of its proper divisors (1).

78921581 is an equidigital number, since it uses as much as digits as its factorization.

78921581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 40320, while the sum is 41.

The square root of 78921581 is about 8883.7819086243. The cubic root of 78921581 is about 428.9420195747.

The spelling of 78921581 in words is "seventy-eight million, nine hundred twenty-one thousand, five hundred eighty-one".