Search: id:A000644 Results 1-1 of 1 results found. %I A000644 %S A000644 1,1,3,7,31,138,808,4956,33047,227328 %N A000644 Loops of length 4n on square grid that turn at each step and return to start in original direction. %D A000644 D. E. Knuth, The Texbook, p. 390. %D A000644 D. E. Knuth, personal communication. %Y A000644 Sequence in context: A123488 A121620 A042271 this_sequence A015459 A115083 A141385 %Y A000644 Adjacent sequences: A000641 A000642 A000643 this_sequence A000645 A000646 A000647 %K A000644 nonn,nice %O A000644 0,3 %A A000644 N. J. A. Sloane (njas(AT)research.att.com). Search completed in 0.001 seconds