A092369 Spiro-tetranacci numbers: a(n) = sum of four previous terms that are nearest when terms arranged in a spiral.

0, 1, 1, 1, 3, 5, 9, 15, 25, 41, 68, 111, 181, 294, 299, 597, 900, 1505, 1522, 3041, 4577, 7642, 7691, 7772, 15529, 23367, 39005, 39225, 39585, 79102, 118979, 198556, 199330, 200520, 202316, 404333, 608146, 1013976, 1017903, 1023971, 1033111

Offset

0,5

Links

Table of n, a(n) for n=0..40.

Example

Terms are written in square boxes radiating spirally (cf. Ulam prime spiral). a(0) = 0, a(1) = 1, a(2) = 1 and a(3) = 1, so write 0, then 1 to its right, another 1 below the first 1 and another to the left of that. The next unfilled box forms an incomplete rectangle with the four filled boxes, so a(4) = a(0) + a(1) + a(2) + a(3) = 0 + 1 + 1 + 1 = 3. The next unfilled box forms the complete rectangle with the filled boxes. Since a(2) is nearer than a(3), a(5) = a(0) + a(1) + a(3) + a(4) = 0 + 1 + 3 + 5 = 9. In the case of a tie in nearness, the chronologically nearer value is used.

Crossrefs

Cf. A078510, A092360.

Sequence in context: A053521 A128587 A001595 * A298340 A061969 A034084

Adjacent sequences: A092366 A092367 A092368 * A092370 A092371 A092372

Keyword

easy,nonn

Author

Michael Joseph Halm, Apr 02 2004

Status

approved