

A231965


Smallest integer starting a group of exactly n consecutive untouchable numbers (A005114) with term differences of 2.


3



246, 288, 892, 9020, 11456, 23480, 52274, 33686, 190070, 1741856, 1668564, 7806762
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OFFSET

2,1


COMMENTS

Such ntuplets from A005114 correspond to n+1 positive numbers interspersed with n zeros in A070015, and starting at a(n)  1. For instance, a(4) = 892 is related to A070015(891) and consecutive values: 2661, 0, 4147, 0, 2945, 0, 1287, 0, 9757.


LINKS

Table of n, a(n) for n=2..13.
Eric Weisstein's World of Mathematics, Untouchable Number.
Wikipedia, Untouchable number


EXAMPLE

a(5) = 9020, because 9020, 9022, 9024, 9026, 9028 are untouchable, while 9018 and 9030 are not so (A001065). For examples with smaller n, see A231964 comments.


PROG

(PARI) oksucc(v, vi, n) = {for (i = 1, n1, if (! vecsearch(v, vi+2*i, ) , return (0)); ); return(! vecsearch(v, vi2) && !vecsearch(v, vi+2*n)); }
a(n) = {v = readvec("untouchable.log"); for (i=1, #v, vi = v[i]; if (oksucc(v, vi, n), return(vi)); ); } \\ readvec reads the file obtained by keeping the second column of b005114.txt seen as a csv file.


CROSSREFS

Cf. A001065, A005114, A231964.
Cf. A110875 (analog for sigma(n)).
Sequence in context: A098195 A214474 A231964 * A067916 A229577 A186796
Adjacent sequences: A231962 A231963 A231964 * A231966 A231967 A231968


KEYWORD

nonn,more


AUTHOR

Michel Marcus, Nov 16 2013


EXTENSIONS

a(10)a(13) from Donovan Johnson, Nov 16 2013
Definition, data, and Pari script corrected by Michel Marcus with Donovan Johnson, Nov 18 2013


STATUS

approved



