It is a congruent number.
It is an unprimeable number.
Almost surely, 221661465732412 is an apocalyptic number.
21661465732412 is a gapful number since it is divisible by the number (22) formed by its first and last digit.
It is an amenable number.
21661465732412 is a wasteful number, since it uses less digits than its factorization.
21661465732412 is an evil number, because the sum of its binary digits is even.
The spelling of 21661465732412 in words is "twenty-one trillion, six hundred sixty-one billion, four hundred sixty-five million, seven hundred thirty-two thousand, four hundred twelve".