21661603 has 4 divisors (see below), whose sum is σ = 21966768. Its totient is φ = 21356440.

The previous prime is 21661597. The next prime is 21661609. The reversal of 21661603 is 30616612.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21661597) and next prime (21661609).

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21661603 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21661609) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 152476 + ... + 152617.

It is an arithmetic number, because the mean of its divisors is an integer number (5491692).

Almost surely, 2^21661603 is an apocalyptic number.

21661603 is a deficient number, since it is larger than the sum of its proper divisors (305165).

21661603 is an equidigital number, since it uses as much as digits as its factorization.

21661603 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 305164.

The product of its (nonzero) digits is 1296, while the sum is 25.

The square root of 21661603 is about 4654.2027244202. The cubic root of 21661603 is about 278.7598340890.

The spelling of 21661603 in words is "twenty-one million, six hundred sixty-one thousand, six hundred three".