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A225619 Composite numbers that remain composite if any digit is deleted (zero and one are not considered prime). 1
44, 46, 48, 49, 64, 66, 68, 69, 84, 86, 88, 94, 96, 98, 99, 104, 106, 108, 120, 122, 124, 125, 126, 128, 140, 142, 144, 145, 146, 148, 150, 152, 154, 155, 156, 158, 160, 162, 164, 165, 166, 168, 180, 182, 184, 185, 186, 188, 204, 206, 208, 210, 212, 214, 215 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

These are sometimes called "deletable composites".

LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000

Dave Radcliffe, Python program/code

EXAMPLE

142 is composite. If the 1 is deleted, 42 is composite. If the 4 is deleted, 12 is composite. If the 2 is deleted, 14 is composite. Therefore, 142 is included in this sequence.

MATHEMATICA

prime01Q[n_] := n == 0 || n == 1 || PrimeQ[n]; okQ[n_] := Module[{d = IntegerDigits[n]}, Not[Or @@ prime01Q /@ Table[FromDigits[Delete[d, i]], {i, Length[d]}]]]; Select[Range[215], ! PrimeQ[#] && okQ[#] &] (* T. D. Noe, Aug 14 2013 *)

CROSSREFS

Cf. A202262 (composite numbers in which all substrings are composite).

Sequence in context: A242934 A038400 A254750 * A121610 A254752 A063837

Adjacent sequences:  A225616 A225617 A225618 * A225620 A225621 A225622

KEYWORD

nonn,base,easy

AUTHOR

Derek Orr, Aug 04 2013

STATUS

approved

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Last modified February 20 00:28 EST 2019. Contains 320329 sequences. (Running on oeis4.)