31218661 has 2 divisors, whose sum is σ = 31218662. Its totient is φ = 31218660.

The previous prime is 31218599. The next prime is 31218673. The reversal of 31218661 is 16681213.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 23961025 + 7257636 = 4895^2 + 2694^2 .

It is an emirp because it is prime and its reverse (16681213) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 31218661 - 2¹⁵ = 31185893 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (31218361) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15609330 + 15609331.

It is an arithmetic number, because the mean of its divisors is an integer number (15609331).

Almost surely, 2^31218661 is an apocalyptic number.

It is an amenable number.

31218661 is a deficient number, since it is larger than the sum of its proper divisors (1).

31218661 is an equidigital number, since it uses as much as digits as its factorization.

31218661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1728, while the sum is 28.

The square root of 31218661 is about 5587.3661952659. The cubic root of 31218661 is about 314.8749348146.

Adding to 31218661 its reverse (16681213), we get a palindrome (47899874).

The spelling of 31218661 in words is "thirty-one million, two hundred eighteen thousand, six hundred sixty-one".