21981501 has 6 divisors (see below), whose sum is σ = 31751070. Its totient is φ = 14654328.

The previous prime is 21981497. The next prime is 21981559. The reversal of 21981501 is 10518912.

It can be written as a sum of positive squares in only one way, i.e., 18922500 + 3059001 = 4350^2 + 1749^2 .

It is not a de Polignac number, because 21981501 - 2² = 21981497 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21981301) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1221186 + ... + 1221203.

It is an arithmetic number, because the mean of its divisors is an integer number (5291845).

Almost surely, 2^21981501 is an apocalyptic number.

It is an amenable number.

21981501 is a deficient number, since it is larger than the sum of its proper divisors (9769569).

21981501 is a wasteful number, since it uses less digits than its factorization.

21981501 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2442395 (or 2442392 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 27.

The square root of 21981501 is about 4688.4433450773. The cubic root of 21981501 is about 280.1253732760.

The spelling of 21981501 in words is "twenty-one million, nine hundred eighty-one thousand, five hundred one".