21661372 has 6 divisors (see below), whose sum is σ = 37907408. Its totient is φ = 10830684.

The previous prime is 21661357. The next prime is 21661397. The reversal of 21661372 is 27316612.

It is a plaindrome in base 11.

It is a self number, because there is not a number n which added to its sum of digits gives 21661372.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2707668 + ... + 2707675.

Almost surely, 2^21661372 is an apocalyptic number.

It is an amenable number.

21661372 is a deficient number, since it is larger than the sum of its proper divisors (16246036).

21661372 is a wasteful number, since it uses less digits than its factorization.

21661372 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5415347 (or 5415345 counting only the distinct ones).

The product of its digits is 3024, while the sum is 28.

The square root of 21661372 is about 4654.1779080736. The cubic root of 21661372 is about 278.7588431844.

Adding to 21661372 its reverse (27316612), we get a palindrome (48977984).

The spelling of 21661372 in words is "twenty-one million, six hundred sixty-one thousand, three hundred seventy-two".