id:A072732 - OEIS Search Results

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Simple triangle-stretching N X N -> N bijection: push terms in the middle twice as far down to make space for the terms obtained by bisecting the edges, which are thus contracted by the same factor. Do this for all "triangle-shells" successively contained inside each other in A001477.

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0, 1, 4, 7, 12, 2, 3, 17, 24, 8, 11, 31, 40, 18, 5, 6, 23, 49, 60, 32, 13, 16, 39, 71, 84, 50, 25, 9, 10, 30, 59, 97, 112, 72, 41, 19, 22, 48, 83, 127, 144, 98, 61, 33, 14, 15, 38, 70, 111, 161, 180, 128, 85, 51, 26, 29, 58, 96, 143, 199, 220, 162, 113, 73, 42, 20, 21, 47 (list; table; graph; listen)

	OFFSET	`0,3`
	LINKS	`Index entries for sequences that are permutations of the natural numbers`
	PROGRAM	`(Scheme) (define (A072732 n) (packA072732 (A025581 n) (A002262 n)))` `(define (packA001477 x y) (/ (+ (expt (+ x y) 2) x (* 3 y)) 2))` `(define (packA072732 x y) (let ((x-y (- x y))) (cond ((<= x-y 0) (packA001477 (+ (* 2 x) (modulo x-y 2)) (+ (* 2 x) (floor->exact (/ (1+ (- x-y)) 2))))) (else (packA001477 (+ (* 2 (1+ y)) (floor->exact (/ (- x-y 2) 2))) (+ (* 2 y) (modulo (1+ x-y) 2)))))))`
	CROSSREFS	`Inverse: A072733, projections: A072736 & A072737, variant of the same theme: A072734. Cf. also A001477 and its projections A025581 & A002262.` `Sequence in context: A074705 A128836 A061956 this_sequence A083487 A092572 A092574` `Adjacent sequences: A072729 A072730 A072731 this_sequence A072733 A072734 A072735`
	KEYWORD	`nonn,tabl`
	AUTHOR	`Antti Karttunen Jun 12 2002`

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Last modified August 19 23:53 EDT 2008. Contains 142930 sequences.

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