OFFSET
1,1
LINKS
Sean A. Irvine, Table of n, a(n) for n = 1..53 (terms 1..33 from Giovanni Resta)
EXAMPLE
a(4) = 9216 as 9, 2, 1, 6 have alternating parity.
MAPLE
alp:= proc(n) local L, d;
L:= convert(n, base, 10);
d:= nops(L);
if d::even then L:= L + map(op, [[0, 1]$(d/2)]) else L:= L + map(op, [[0, 1]$((d-1)/2), [0]]) fi;
nops(convert(L mod 2, set))=1
end proc:f:= proc(d) local s;
for s from floor(sqrt(10^d)) by -1 to ceil(sqrt(10^(d-1))) do
if alp(s^2) then return s^2 fi
od;
0
end proc:map(f, [$1..10]); # Robert Israel, Aug 14 2018
MATHEMATICA
altQ[n_] := n < 10 || Union[Total /@ Partition[ Mod[ IntegerDigits@ n, 2], 2, 1]] == {1}; a[n_] := Block[{r = Floor@ Sqrt@ FromDigits[8 + Mod[ Range@ n, 2]]}, While[! altQ[r^2], r--]; r^2]; Array[a, 16] (* Giovanni Resta, Aug 17 2018 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Mar 19 2002
EXTENSIONS
a(5) corrected and more terms from Robert Israel, Aug 14 2018
a(18)-a(20) from Giovanni Resta, Aug 16 2018
STATUS
approved