31386781 has 2 divisors, whose sum is σ = 31386782. Its totient is φ = 31386780.

The previous prime is 31386749. The next prime is 31386793. The reversal of 31386781 is 18768313.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16687225 + 14699556 = 4085^2 + 3834^2 .

It is a cyclic number.

It is not a de Polignac number, because 31386781 - 2⁵ = 31386749 is a prime.

It is a super-2 number, since 2×31386781² = 1970260043083922, which contains 22 as substring.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 31386781.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (31386181) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15693390 + 15693391.

It is an arithmetic number, because the mean of its divisors is an integer number (15693391).

Almost surely, 2^31386781 is an apocalyptic number.

It is an amenable number.

31386781 is a deficient number, since it is larger than the sum of its proper divisors (1).

31386781 is an equidigital number, since it uses as much as digits as its factorization.

31386781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 24192, while the sum is 37.

The square root of 31386781 is about 5602.3906504277. The cubic root of 31386781 is about 315.4391489723.

The spelling of 31386781 in words is "thirty-one million, three hundred eighty-six thousand, seven hundred eighty-one".