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10-digit numbers by digits 1, 2, 3 (HOMC 2016 S Q1)

Source:

September 8, 2019

number theoryDigits

Problem Statement

How many are there

10

-digit numbers composed from the digits

1, 2, 3

only and in which, two neighbouring digits differ by

1

:
(A):

48

(B):

64

(C):

72

(D):

128

(E): None of the above.