A225619 Composite numbers that remain composite if any digit is deleted (zero and one are not considered prime).

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

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: A038400 A364657 A254750 * A121610 A254752 A178755

Adjacent sequences: A225616 A225617 A225618 * A225620 A225621 A225622

Keyword

nonn,base,easy

Author

Derek Orr, Aug 04 2013

Status

approved