21525551 has 2 divisors, whose sum is σ = 21525552. Its totient is φ = 21525550.

The previous prime is 21525547. The next prime is 21525571. The reversal of 21525551 is 15552512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21525551 - 2² = 21525547 is a prime.

It is a Sophie Germain prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21525551.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21525541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10762775 + 10762776.

It is an arithmetic number, because the mean of its divisors is an integer number (10762776).

Almost surely, 2^21525551 is an apocalyptic number.

21525551 is a deficient number, since it is larger than the sum of its proper divisors (1).

21525551 is an equidigital number, since it uses as much as digits as its factorization.

21525551 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2500, while the sum is 26.

The square root of 21525551 is about 4639.5636648288. The cubic root of 21525551 is about 278.1749972146.

The spelling of 21525551 in words is "twenty-one million, five hundred twenty-five thousand, five hundred fifty-one".