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
Martin Janecke, Table of n, a(n) for n = 1..10000
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
KEYWORD
easy,nonn
AUTHOR
Martin Janecke, Jan 14 2017
STATUS
approved