31920373781 has 2 divisors, whose sum is σ = 31920373782. Its totient is φ = 31920373780.

The previous prime is 31920373757. The next prime is 31920373789. The reversal of 31920373781 is 18737302913.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 24284235556 + 7636138225 = 155834^2 + 87385^2 .

It is a cyclic number.

It is not a de Polignac number, because 31920373781 - 2¹⁴ = 31920357397 is a prime.

It is a super-2 number, since 2×31920373781² (a number of 22 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (31920373789) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15960186890 + 15960186891.

It is an arithmetic number, because the mean of its divisors is an integer number (15960186891).

Almost surely, 2^31920373781 is an apocalyptic number.

It is an amenable number.

31920373781 is a deficient number, since it is larger than the sum of its proper divisors (1).

31920373781 is an equidigital number, since it uses as much as digits as its factorization.

31920373781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 190512, while the sum is 44.

The spelling of 31920373781 in words is "thirty-one billion, nine hundred twenty million, three hundred seventy-three thousand, seven hundred eighty-one".