21545501 has 2 divisors, whose sum is σ = 21545502. Its totient is φ = 21545500.

The previous prime is 21545479. The next prime is 21545509. The reversal of 21545501 is 10554512.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12243001 + 9302500 = 3499^2 + 3050^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21545501 is a prime.

It is a super-2 number, since 2×21545501² = 928417226682002, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21545509) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10772750 + 10772751.

It is an arithmetic number, because the mean of its divisors is an integer number (10772751).

Almost surely, 2^21545501 is an apocalyptic number.

It is an amenable number.

21545501 is a deficient number, since it is larger than the sum of its proper divisors (1).

21545501 is an equidigital number, since it uses as much as digits as its factorization.

21545501 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1000, while the sum is 23.

The square root of 21545501 is about 4641.7131535673. The cubic root of 21545501 is about 278.2609087222.

The spelling of 21545501 in words is "twenty-one million, five hundred forty-five thousand, five hundred one".