21487 has 2 divisors, whose sum is σ = 21488. Its totient is φ = 21486.
The previous prime is 21481. The next prime is 21491. The reversal of 21487 is 78412.
It is a strong prime.
It is a cyclic number.
It is a de Polignac number, because none of the positive numbers 2k-21487 is a prime.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (21481) by changing a digit.
It is a pernicious number, because its binary representation contains a prime number (11) of ones.
It is a good prime.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10743 + 10744.
It is an arithmetic number, because the mean of its divisors is an integer number (10744).
221487 is an apocalyptic number.
21487 is a deficient number, since it is larger than the sum of its proper divisors (1).
21487 is an equidigital number, since it uses as much as digits as its factorization.
21487 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 448, while the sum is 22.
The square root of 21487 is about 146.5844466511. The cubic root of 21487 is about 27.8008832941.
Adding to 21487 its reverse (78412), we get a palindrome (99899).
The spelling of 21487 in words is "twenty-one thousand, four hundred eighty-seven".
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