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A231964 Lesser member of untouchable twin pairs, that is, such that a(n) and a(n)+2 are untouchable (A005114). 8
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
Eric Weisstein's World of Mathematics, 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
Sequence in context: A023097 A098195 A214474 * A231965 A067916 A229577
KEYWORD
nonn
AUTHOR
Michel Marcus, Nov 16 2013
STATUS
approved

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Last modified March 29 01:36 EDT 2024. Contains 371264 sequences. (Running on oeis4.)