78281221 has 2 divisors, whose sum is σ = 78281222. Its totient is φ = 78281220.

The previous prime is 78281219. The next prime is 78281249. The reversal of 78281221 is 12218287.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 76562500 + 1718721 = 8750^2 + 1311^2 .

It is a cyclic number.

It is not a de Polignac number, because 78281221 - 2¹ = 78281219 is a prime.

It is a super-2 number, since 2×78281221² = 12255899122501682, which contains 22 as substring.

Together with 78281219, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78281321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39140610 + 39140611.

It is an arithmetic number, because the mean of its divisors is an integer number (39140611).

Almost surely, 2^78281221 is an apocalyptic number.

It is an amenable number.

78281221 is a deficient number, since it is larger than the sum of its proper divisors (1).

78281221 is an equidigital number, since it uses as much as digits as its factorization.

78281221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3584, while the sum is 31.

The square root of 78281221 is about 8847.6675457433. The cubic root of 78281221 is about 427.7787400489.

The spelling of 78281221 in words is "seventy-eight million, two hundred eighty-one thousand, two hundred twenty-one".