# 78 (number)

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78 (number)

78 (seventy-eight) is the natural number following 77 and followed by 79.

78
Cardinal seventy-eight
Ordinal 78th
(seventy-eighth)
Numeral system 78
Factorization $2 \cdot 3 \cdot 13$
Divisors 1, 2, 3, 6, 13, 26, 39, 78
Roman numeral LXXVIII
Binary 10011102
Octal 1168
Duodecimal 6612

## In mathematics

78 is a triangular number, and its factorization makes it a sphenic number. As a multiple of a perfect number, 78 is itself a semiperfect number.

77 and 78 form a Ruth-Aaron pair under the second definition in which repeated prime factors are counted as often as they occur.

Since it is possible to find sequences of 78 consecutive integers such that each inner member shares a factor with either the first or the last member, 78 is an Erdős–Woods number.

Karl A. Dahlke proved in 1989 that 78 heptominos of this shape ( ), at a minimum, are required to fill a rectangle.

78 is also:

## References

1. ^ "Both wolves and dogs possess 78 chromosomes." Handbook of Applied Dog Behavior and Training by Steven R. Lindsay, Wiley-Blackwell (2000) p. 11

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