A231964 Lesser member of untouchable twin pairs, that is, such that a(n) and a(n)+2 are untouchable (A005114).

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

Offset: 1

Author

Michel Marcus, Nov 16 2013

Keywords

• nonn

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.

Examples

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

Links

• Donovan Johnson, Table of n, a(n) for n = 1..10000
• Eric Weisstein's World of Mathematics, Untouchable Number.
• Wikipedia, Untouchable number

Crossrefs

Cf. A005114, A231965.

Programs

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