21001945 has 16 divisors (see below), whose sum is σ = 26223120. Its totient is φ = 16128000.

The previous prime is 21001943. The next prime is 21001961. The reversal of 21001945 is 54910012.

It can be written as a sum of positive squares in 8 ways, for example, as 1394761 + 19607184 = 1181^2 + 4428^2 .

It is not a de Polignac number, because 21001945 - 2¹ = 21001943 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21001943) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 34645 + ... + 35245.

It is an arithmetic number, because the mean of its divisors is an integer number (1638945).

Almost surely, 2^21001945 is an apocalyptic number.

It is an amenable number.

21001945 is a deficient number, since it is larger than the sum of its proper divisors (5221175).

21001945 is a wasteful number, since it uses less digits than its factorization.

21001945 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 876.

The product of its (nonzero) digits is 360, while the sum is 22.

The square root of 21001945 is about 4582.7879069405. The cubic root of 21001945 is about 275.9009350061.

Adding to 21001945 its reverse (54910012), we get a palindrome (75911957).

The spelling of 21001945 in words is "twenty-one million, one thousand, nine hundred forty-five".