21539149 has 2 divisors, whose sum is σ = 21539150. Its totient is φ = 21539148.

The previous prime is 21539137. The next prime is 21539183. The reversal of 21539149 is 94193512.

It is an a-pointer prime, because the next prime (21539183) can be obtained adding 21539149 to its sum of digits (34).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11009124 + 10530025 = 3318^2 + 3245^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21539149 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21539449) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10769574 + 10769575.

It is an arithmetic number, because the mean of its divisors is an integer number (10769575).

Almost surely, 2^21539149 is an apocalyptic number.

It is an amenable number.

21539149 is a deficient number, since it is larger than the sum of its proper divisors (1).

21539149 is an equidigital number, since it uses as much as digits as its factorization.

21539149 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9720, while the sum is 34.

The square root of 21539149 is about 4641.0288729979. The cubic root of 21539149 is about 278.2335605994.

It can be divided in two parts, 21539 and 149, that multiplied together give a triangular number (3209311 = T₂₅₃₃).

The spelling of 21539149 in words is "twenty-one million, five hundred thirty-nine thousand, one hundred forty-nine".