78217621 has 2 divisors, whose sum is σ = 78217622. Its totient is φ = 78217620.

The previous prime is 78217597. The next prime is 78217631. The reversal of 78217621 is 12671287.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 59120721 + 19096900 = 7689^2 + 4370^2 .

It is an emirp because it is prime and its reverse (12671287) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 78217621 - 2⁹ = 78217109 is a prime.

It is a super-2 number, since 2×78217621² = 12235992469799282, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78217631) 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, 39108810 + 39108811.

It is an arithmetic number, because the mean of its divisors is an integer number (39108811).

Almost surely, 2^78217621 is an apocalyptic number.

It is an amenable number.

78217621 is a deficient number, since it is larger than the sum of its proper divisors (1).

78217621 is an equidigital number, since it uses as much as digits as its factorization.

78217621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9408, while the sum is 34.

The square root of 78217621 is about 8844.0726478246. The cubic root of 78217621 is about 427.6628582792.

The spelling of 78217621 in words is "seventy-eight million, two hundred seventeen thousand, six hundred twenty-one".