21431681 has 2 divisors, whose sum is σ = 21431682. Its totient is φ = 21431680.

The previous prime is 21431647. The next prime is 21431701. The reversal of 21431681 is 18613412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19891600 + 1540081 = 4460^2 + 1241^2 .

It is a cyclic number.

It is not a de Polignac number, because 21431681 - 2¹⁸ = 21169537 is a prime.

It is a super-2 number, since 2×21431681² = 918633900971522, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21431681.

It is not a weakly prime, because it can be changed into another prime (21433681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10715840 + 10715841.

It is an arithmetic number, because the mean of its divisors is an integer number (10715841).

Almost surely, 2^21431681 is an apocalyptic number.

It is an amenable number.

21431681 is a deficient number, since it is larger than the sum of its proper divisors (1).

21431681 is an equidigital number, since it uses as much as digits as its factorization.

21431681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1152, while the sum is 26.

The square root of 21431681 is about 4629.4363587806. The cubic root of 21431681 is about 277.7700468900.

The spelling of 21431681 in words is "twenty-one million, four hundred thirty-one thousand, six hundred eighty-one".