The pattern appears to be that the sum of the numbers in any three connected circles is 10. For the top diamond: 5+4+1=10. For the right diamond: 1+2+?=10 -> ?=7. For the bottom diamond: 3+4+?=10 -> ?=3. Let's assume the pattern is that the sum of the three vertices of any small triangle is 10. For the bottom right vertex, 3+4+?=10 -> ?=3.