21543961 has 2 divisors, whose sum is σ = 21543962. Its totient is φ = 21543960.

The previous prime is 21543931. The next prime is 21544009. The reversal of 21543961 is 16934512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19527561 + 2016400 = 4419^2 + 1420^2 .

It is a cyclic number.

It is not a de Polignac number, because 21543961 - 2¹¹ = 21541913 is a prime.

It is not a weakly prime, because it can be changed into another prime (21543911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10771980 + 10771981.

It is an arithmetic number, because the mean of its divisors is an integer number (10771981).

Almost surely, 2^21543961 is an apocalyptic number.

It is an amenable number.

21543961 is a deficient number, since it is larger than the sum of its proper divisors (1).

21543961 is an equidigital number, since it uses as much as digits as its factorization.

21543961 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6480, while the sum is 31.

The square root of 21543961 is about 4641.5472635749. The cubic root of 21543961 is about 278.2542788460.

The spelling of 21543961 in words is "twenty-one million, five hundred forty-three thousand, nine hundred sixty-one".