18977221 has 2 divisors, whose sum is σ = 18977222. Its totient is φ = 18977220.

The previous prime is 18977209. The next prime is 18977249. The reversal of 18977221 is 12277981.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16769025 + 2208196 = 4095^2 + 1486^2 .

It is an emirp because it is prime and its reverse (12277981) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18977221 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18977201) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9488610 + 9488611.

It is an arithmetic number, because the mean of its divisors is an integer number (9488611).

Almost surely, 2^18977221 is an apocalyptic number.

It is an amenable number.

18977221 is a deficient number, since it is larger than the sum of its proper divisors (1).

18977221 is an equidigital number, since it uses as much as digits as its factorization.

18977221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 14112, while the sum is 37.

The square root of 18977221 is about 4356.2852294128. The cubic root of 18977221 is about 266.7334844716.

The spelling of 18977221 in words is "eighteen million, nine hundred seventy-seven thousand, two hundred twenty-one".