21781603 has 2 divisors, whose sum is σ = 21781604. Its totient is φ = 21781602.

The previous prime is 21781601. The next prime is 21781609. The reversal of 21781603 is 30618712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21781603 - 2¹ = 21781601 is a prime.

Together with 21781601, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21781601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10890801 + 10890802.

It is an arithmetic number, because the mean of its divisors is an integer number (10890802).

Almost surely, 2^21781603 is an apocalyptic number.

21781603 is a deficient number, since it is larger than the sum of its proper divisors (1).

21781603 is an equidigital number, since it uses as much as digits as its factorization.

21781603 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2016, while the sum is 28.

The square root of 21781603 is about 4667.0764939092. The cubic root of 21781603 is about 279.2736403085.

The spelling of 21781603 in words is "twenty-one million, seven hundred eighty-one thousand, six hundred three".