21905501 has 2 divisors, whose sum is σ = 21905502. Its totient is φ = 21905500.

The previous prime is 21905497. The next prime is 21905519. The reversal of 21905501 is 10550912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21576025 + 329476 = 4645^2 + 574^2 .

It is a cyclic number.

It is not a de Polignac number, because 21905501 - 2² = 21905497 is a prime.

It is a super-2 number, since 2×21905501² = 959701948122002, 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 (21905531) 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, 10952750 + 10952751.

It is an arithmetic number, because the mean of its divisors is an integer number (10952751).

Almost surely, 2^21905501 is an apocalyptic number.

It is an amenable number.

21905501 is a deficient number, since it is larger than the sum of its proper divisors (1).

21905501 is an equidigital number, since it uses as much as digits as its factorization.

21905501 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 450, while the sum is 23.

The square root of 21905501 is about 4680.3312916929. The cubic root of 21905501 is about 279.8021604155.

The spelling of 21905501 in words is "twenty-one million, nine hundred five thousand, five hundred one".