31781861 has 2 divisors, whose sum is σ = 31781862. Its totient is φ = 31781860.

The previous prime is 31781843. The next prime is 31781873. The reversal of 31781861 is 16818713.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 30459361 + 1322500 = 5519^2 + 1150^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-31781861 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (31781831) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15890930 + 15890931.

It is an arithmetic number, because the mean of its divisors is an integer number (15890931).

Almost surely, 2^31781861 is an apocalyptic number.

It is an amenable number.

31781861 is a deficient number, since it is larger than the sum of its proper divisors (1).

31781861 is an equidigital number, since it uses as much as digits as its factorization.

31781861 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8064, while the sum is 35.

The square root of 31781861 is about 5637.5403324500. The cubic root of 31781861 is about 316.7571605944.

The spelling of 31781861 in words is "thirty-one million, seven hundred eighty-one thousand, eight hundred sixty-one".