21905531 has 2 divisors, whose sum is σ = 21905532. Its totient is φ = 21905530.

The previous prime is 21905519. The next prime is 21905573. The reversal of 21905531 is 13550912.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21905531 is a prime.

It is a super-2 number, since 2×21905531² = 959704576783922, 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 21905531.

It is not a weakly prime, because it can be changed into another prime (21905501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10952765 + 10952766.

It is an arithmetic number, because the mean of its divisors is an integer number (10952766).

Almost surely, 2^21905531 is an apocalyptic number.

21905531 is a deficient number, since it is larger than the sum of its proper divisors (1).

21905531 is an equidigital number, since it uses as much as digits as its factorization.

21905531 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1350, while the sum is 26.

The square root of 21905531 is about 4680.3344965932. The cubic root of 21905531 is about 279.8022881469.

The spelling of 21905531 in words is "twenty-one million, nine hundred five thousand, five hundred thirty-one".