21542663 has 2 divisors, whose sum is σ = 21542664. Its totient is φ = 21542662.

The previous prime is 21542639. The next prime is 21542681. The reversal of 21542663 is 36624512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21542663 - 2¹² = 21538567 is a prime.

It is equal to p_1362098 and since 21542663 and 1362098 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21542623) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10771331 + 10771332.

It is an arithmetic number, because the mean of its divisors is an integer number (10771332).

Almost surely, 2^21542663 is an apocalyptic number.

21542663 is a deficient number, since it is larger than the sum of its proper divisors (1).

21542663 is an equidigital number, since it uses as much as digits as its factorization.

21542663 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8640, while the sum is 29.

The square root of 21542663 is about 4641.4074374052. The cubic root of 21542663 is about 278.2486905622.

The spelling of 21542663 in words is "twenty-one million, five hundred forty-two thousand, six hundred sixty-three".