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A250041 Numbers n such that m = floor(n/10) is not coprime to n and, if nonzero, m is also a term of the sequence. 9
2, 3, 4, 5, 6, 7, 8, 9, 20, 22, 24, 26, 28, 30, 33, 36, 39, 40, 42, 44, 46, 48, 50, 55, 60, 62, 63, 64, 66, 68, 69, 70, 77, 80, 82, 84, 86, 88, 90, 93, 96, 99, 200, 202, 204, 205, 206, 208, 220, 222, 224, 226, 228, 240, 242, 243, 244, 246, 248, 249, 260, 262 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Equivalent definition 1: Assuming a base b (in this case b=10), let us say that a positive integer k has the property RTNC(b) when m=floor(k/b) is not coprime to k, i.e., gcd(k,m)>1. Then k belongs to this sorted list if (i) it has the property RTNC(b) and (ii) m is either 0 or belongs also to the list.

Equivalent definition 2: Every nonempty prefix of a(n) in base b has the property RTNC(b).

Notes: The acronym RTNC stands for 'Right-Truncated is Not Coprime' (negation of the property RTC defined in A250040). We could also say that a(n) are right-truncatable numbers with property RTNC(b).

This particular list is an infinite subset of A248500.

LINKS

Stanislav Sykora, Table of n, a(n) for n = 1..10000

Stanislav Sykora, PARI/GP scripts for genetic threads, with code and comments.

Wikipedia, Coprime integers

EXAMPLE

243 is a member because (243,24), (24,2) and (2,0) are noncoprime pairs.

155 is not a member because gcd(15,1)=1.

PROG

(PARI) See the link.

(PARI) is_rtnc(n, b=10) = {while (((m=gcd(n\b, n)) != 1), if (m == 0, return (1)); n = n\b; ); return (0); } \\ Michel Marcus, Jan 29 2015

CROSSREFS

Cf. A248500, A250040.

Other lists of right-truncatable numbers with the property RTNC(b): A005823 (b=3), A250037 (b=4), A250039 (b=16), A250043 (b=9), A250045 (b=8), A250047 (b=7), A250049 (b=6), A250051 (b=5).

Sequence in context: A110803 A109795 A248500 * A132029 A281724 A217489

Adjacent sequences:  A250038 A250039 A250040 * A250042 A250043 A250044

KEYWORD

nonn,base

AUTHOR

Stanislav Sykora, Dec 07 2014

STATUS

approved

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Last modified June 28 16:43 EDT 2017. Contains 288839 sequences.