21651591 has 32 divisors (see below), whose sum is σ = 33324480. Its totient is φ = 12429312.

The previous prime is 21651589. The next prime is 21651593. The reversal of 21651591 is 19515612.

It is an interprime number because it is at equal distance from previous prime (21651589) and next prime (21651593).

It is not a de Polignac number, because 21651591 - 2¹ = 21651589 is a prime.

Its product of digits (2700) is a multiple of the sum of its prime factors (180).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21651593) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 191551 + ... + 191663.

It is an arithmetic number, because the mean of its divisors is an integer number (1041390).

Almost surely, 2^21651591 is an apocalyptic number.

21651591 is a deficient number, since it is larger than the sum of its proper divisors (11672889).

21651591 is a wasteful number, since it uses less digits than its factorization.

21651591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 180 (or 146 counting only the distinct ones).

The product of its digits is 2700, while the sum is 30.

The square root of 21651591 is about 4653.1270130956. The cubic root of 21651591 is about 278.7168798417.

The spelling of 21651591 in words is "twenty-one million, six hundred fifty-one thousand, five hundred ninety-one".