You’ll have to go and read the post to find out what makes a number “happy” 🙂
Perhaps it’s unsurprising that 7 is the second happy number (after 1). All those years of being regarded as exceptionally lucky have obviously done a lot for its self-esteem. While I don’t quite comprehend why 7 is deemed so lucky (or why rabbits’ feet are considered lucky, I’m fairly confident the rabbit felt it was luckier attached to its leg) but it’s obviously quite pleased with the state of affairs. Interestingly 13 is also happy, not a twinge of guilt for all the bad luck it has bestowed on people.