The pattern relates consecutive primes: 13 and 17 are consecutive primes. Their sum is 30, and the next prime after 17 is 19. 30-11(prime) = 19. But this doesn't clearly yield 61. Another pattern: 13→17 (next prime), 59→61 (next prime). Both 13 and 59 are primes, and 17 and 61 are the immediately following primes.