21503 has 2 divisors, whose sum is σ = 21504.
Its totient is φ = 21502.
The previous prime is 21499. The next prime is 21517. The reversal of 21503 is 30512.
It is a weak prime.
It is a cyclic number.
It is not a de Polignac number, because 21503 - 22 = 21499 is a prime.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (21523) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10751 + 10752.
It is an arithmetic number, because the mean of its divisors is an integer number (10752).
221503 is an apocalyptic number.
21503 is a deficient number, since it is larger than the sum of its proper divisors (1).
21503 is an equidigital number, since it uses as much as digits as its factorization.
21503 is an evil number, because the sum of its binary digits is even.
The product of its (nonzero) digits is 30, while the sum is 11.
The square root of 21503 is about 146.6390125444.
The cubic root of 21503 is about 27.8077820975.
Subtracting 21503 from its reverse (30512), we obtain a palindrome (9009).
The spelling of 21503 in words is "twenty-one thousand, five hundred three".