21511000661551 has 8 divisors (see below), whose sum is σ = 21752704467104. Its totient is φ = 21269928762720.

The previous prime is 21511000661461. The next prime is 21511000661599. The reversal of 21511000661551 is 15516600011512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21511000661551 - 2²¹ = 21510998564399 is a prime.

It is a super-2 number, since 2×21511000661551² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21511000661351) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 157908216 + ... + 158044381.

It is an arithmetic number, because the mean of its divisors is an integer number (2719088058388).

Almost surely, 2^{21511000661551} is an apocalyptic number.

21511000661551 is a deficient number, since it is larger than the sum of its proper divisors (241703805553).

21511000661551 is a wasteful number, since it uses less digits than its factorization.

21511000661551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 315953361.

The product of its (nonzero) digits is 9000, while the sum is 34.

The spelling of 21511000661551 in words is "twenty-one trillion, five hundred eleven billion, six hundred sixty-one thousand, five hundred fifty-one".