20685631 has 2 divisors, whose sum is σ = 20685632. Its totient is φ = 20685630.

The previous prime is 20685629. The next prime is 20685653. The reversal of 20685631 is 13658602.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20685631 - 2¹ = 20685629 is a prime.

It is a super-2 number, since 2×20685631² = 855790659736322, which contains 22 as substring.

Together with 20685629, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 20685593 and 20685602.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20685601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10342815 + 10342816.

It is an arithmetic number, because the mean of its divisors is an integer number (10342816).

Almost surely, 2^20685631 is an apocalyptic number.

20685631 is the 2877-th centered pentagonal number.

20685631 is a deficient number, since it is larger than the sum of its proper divisors (1).

20685631 is an equidigital number, since it uses as much as digits as its factorization.

20685631 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 8640, while the sum is 31.

The square root of 20685631 is about 4548.1458859628. The cubic root of 20685631 is about 274.5087914389.

It can be divided in two parts, 20685 and 631, that added together give a square (21316 = 146²).

The spelling of 20685631 in words is "twenty million, six hundred eighty-five thousand, six hundred thirty-one".