A061310 Numbers which cannot be reached in the Countdown Numbers Game starting from (1,2,3,4,5,6): the game allows brackets and the operations + - x and / and not all numbers need be used, while the result of each partial calculation must be an integer.

284, 307, 309, 314, 317, 379, 394, 398, 403, 411, 417, 423, 429, 431, 433, 435, 436, 437, 439, 441, 442, 443, 445, 446, 447, 449, 451, 453, 454, 457, 458, 459, 461, 463, 464, 466, 467, 469, 471, 473, 474, 487, 489, 491, 493, 494, 496, 499, 502, 506, 509

Offset

1,1

Comments

Starting with (1,1,1,1,1,1) no number greater than 9 can be reached.

Every number greater than 1080 = 6*5*4*3*(2+1) is in the sequence. - Sean A. Irvine, Feb 07 2023

Links

Michael S. Branicky, Table of n, a(n) for n = 1..538 (all terms < 1081)

Henry Bottomley, Countdown Numbers Game applet

Michael S. Branicky, Python program

Index entries for similar sequences

Index entries for linear recurrences with constant coefficients, signature (2,-1).

Example

283 is not in the sequence since 283=((6+1)*5*4*2)+3; 285 is not in the sequence since 285=((6*5*2)-3)*(4+1). However there is no similar calculation for 284 so 284 is in the sequence.

Crossrefs

Sequence in context: A108826 A285890 A356219 * A333930 A259996 A092681

Adjacent sequences: A061307 A061308 A061309 * A061311 A061312 A061313

Keyword

nonn,easy

Author

Henry Bottomley, Jun 05 2001

Status

approved