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A281071
Largest number k such that b - r is even or r = 0 for all b = 1..k where r = n mod b.
2
1, 2, 1, 4, 1, 6, 1, 2, 1, 10, 1, 4, 1, 2, 1, 6, 1, 6, 1, 2, 1, 4, 1, 4, 1, 2, 1, 10, 1, 6, 1, 2, 1, 4, 1, 12, 1, 2, 1, 8, 1, 4, 1, 2, 1, 6, 1, 6, 1, 2, 1, 4, 1, 4, 1, 2, 1, 6, 1, 6, 1, 2, 1, 4, 1, 14, 1, 2, 1, 10, 1, 4, 1, 2, 1, 6, 1, 8, 1, 2, 1, 4, 1, 4, 1, 2, 1, 6, 1, 6, 1, 2, 1, 4, 1, 8, 1, 2
OFFSET
1,2
COMMENTS
Consider a text mode screen which is a fixed number of character columns wide. Text only breaks at the screen width, there is no manual line break. Then a(n) is the largest screen width in terms of characters so that a string of n printable characters can be perfectly centrally aligned on this and all smaller widths.
a(n) = n for n in {1, 2, 4, 6, 10}, otherwise a(n) < n. The sequence is unbounded.
LINKS
EXAMPLE
a(22) = 4 because
22 mod 1 = 0 where r = 0,
22 mod 2 = 0 where r = 0,
22 mod 3 = 1 where 3 - 1 is even,
22 mod 4 = 2 where 4 - 2 is even, but
22 mod 5 = 2 where r > 0 and 5 - 2 is odd.
PROG
(PARI) a(n) = {ok = 1; k = 1; while(ok, v = vector(k, b, if ((n % b)==0, 0, b - (n%b))); ok = #select(x->((x % 2)==0), v) == k; if (ok, k++); ); k--; } \\ Michel Marcus, Jan 23 2017
CROSSREFS
Cf. A281072.
Sequence in context: A214052 A276094 A247339 * A256908 A346466 A258409
KEYWORD
easy,nonn
AUTHOR
Martin Janecke, Jan 14 2017
STATUS
approved