20631781 has 2 divisors, whose sum is σ = 20631782. Its totient is φ = 20631780.

The previous prime is 20631773. The next prime is 20631797. The reversal of 20631781 is 18713602.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19936225 + 695556 = 4465^2 + 834^2 .

It is a cyclic number.

It is not a de Polignac number, because 20631781 - 2³ = 20631773 is a prime.

It is a super-2 number, since 2×20631781² = 851340774463922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20634781) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10315890 + 10315891.

It is an arithmetic number, because the mean of its divisors is an integer number (10315891).

Almost surely, 2^20631781 is an apocalyptic number.

It is an amenable number.

20631781 is a deficient number, since it is larger than the sum of its proper divisors (1).

20631781 is an equidigital number, since it uses as much as digits as its factorization.

20631781 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2016, while the sum is 28.

The square root of 20631781 is about 4542.2220333225. Note that the first 3 decimals coincide. The cubic root of 20631781 is about 274.2703788523.

It can be divided in two parts, 20631 and 781, that added together give a palindrome (21412).

The spelling of 20631781 in words is "twenty million, six hundred thirty-one thousand, seven hundred eighty-one".