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A231964 Lesser member of untouchable twin pairs, that is, such a(n) and a(n)+2 are untouchable (A005114). 6
246, 288, 290, 304, 322, 324, 406, 472, 516, 518, 624, 626, 668, 748, 766, 782, 802, 892, 894, 896, 934, 964, 1044, 1078, 1146, 1148, 1160, 1246, 1254, 1256, 1312, 1314, 1316, 1346, 1404, 1418, 1420, 1506, 1508, 1680, 1716, 1774, 1820, 1838, 1840, 1842, 1894 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

There are 2673 terms in this sequence when the 8153 terms of A005114, up to 60000, are taken into account.

Note that some numbers come up by pairs like (288,290) or (322,324), corresponding to untouchable triples. Others come up by groups of 3 like (892,894,896) or (1312,1314,1316), corresponding to untouchable quadruplets. For higher n-tuplets, see A231965.

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Untouchable Number.

Wikipedia, Untouchable number

EXAMPLE

246 and 248 are untouchable, so 246 is in this sequence.

PROG

(PARI) lista() = {v = readvec("untouchable.log"); for (i=1, #v, vi = v[i]; if (vecsearch(v, vi+2, ), print1(vi, ", ")); ); } \\ Michel Marcus, Nov 16 2013

CROSSREFS

Cf. A005114, A231965.

Sequence in context: A023097 A098195 A214474 * A231965 A067916 A229577

Adjacent sequences:  A231961 A231962 A231963 * A231965 A231966 A231967

KEYWORD

nonn

AUTHOR

Michel Marcus, Nov 16 2013

STATUS

approved

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Last modified September 28 11:24 EDT 2020. Contains 337393 sequences. (Running on oeis4.)