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A215009 Numbers which are "easy" to key on a computer numpad. 4
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 20, 21, 23, 25, 32, 36, 41, 45, 47, 52, 54, 56, 58, 63, 65, 69, 74, 78, 85, 87, 89, 96, 98, 101, 120, 121, 123, 125, 141, 145, 147, 202, 210, 212, 214, 232, 236, 252, 254, 256, 258, 320, 321, 323, 325, 363, 365, 369, 410 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

On a computer numpad, a number is "easy" to key in if each adjacent pair of digits in the number are adjacent - either horizontally or vertically.

Here are two ways to type these numbers. Example for 25:

1. Press the numpad "2" key. Then let go and press "5".

2. Press the "2" and slide your finger on the numeric keypad up to the "5".

Method 2 shows that the sequence contains only numbers in which every pair of adjacent digits are distinct.

Pressing a numeric key followed by "0" and pressing a numeric key is equivalent to selecting "101" or "202".

LINKS

Arkadiusz Wesolowski, Table of n, a(n) for n = 1..10000

Wikipedia, Numeric keypad

Index entries for 10-automatic sequences.

EXAMPLE

25 is a term because the 2 and 5 keys are adjacent.

MATHEMATICA

lst = {}; Do[If[StringCount[ToString[n], {"00", "03", "04", "05", "06", "07", "08", "09", "11", "13", "15", "16", "17", "18", "19", "22", "24", "26", "27", "28", "29", "30", "31", "33", "34", "35", "37", "38", "39", "40", "42", "43", "44", "46", "48", "49", "50", "51", "53", "55", "57", "59", "60", "61", "62", "64", "66", "67", "68", "70", "71", "72", "73", "75", "76", "77", "79", "80", "81", "82", "83", "84", "86", "88", "90", "91", "92", "93", "94", "95", "97", "99", "102", "201"}] == 0, AppendTo[lst, n]], {n, 0, 410}]; lst

CROSSREFS

Cf. A082390. Subsequence of A043096.

Sequence in context: A322605 A175740 A320321 * A281943 A120003 A036965

Adjacent sequences:  A215006 A215007 A215008 * A215010 A215011 A215012

KEYWORD

base,dumb,easy,nonn

AUTHOR

Arkadiusz Wesolowski, Jul 31 2012

STATUS

approved

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Last modified March 21 10:09 EDT 2019. Contains 321368 sequences. (Running on oeis4.)