This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A181789 #15 Mar 24 2024 10:49:23 %S A181789 183673469387755102041183673469387755102041, %T A181789 326530612244897959184326530612244897959184, %U A181789 734693877551020408164734693877551020408164,132231404958677685950413223140496132231404958677685950413223140496 %N A181789 Pandigital biperiod squares: pandigital squares whose digits repeat twice in order. %C A181789 Ondrejka asks in Problem 1130(b) (see reference) what the smallest biperiod square is in which the ten decimal digits occur equally often (an equipandigital biperiod square), but it remains unknown whether any such square even exists. %D A181789 R. Ondrejka, Problem 1130: Biperiod Squares, Journal of Recreational Mathematics, Vol. 14:4 (1981-82), 299. Solution by F. H. Kierstead, Jr., JRM, Vol. 15:4 (1982-83), 311-312. %H A181789 Chai Wah Wu, <a href="/A181789/b181789.txt">Table of n, a(n) for n = 1..34</a> %o A181789 (Python) %o A181789 from itertools import count, islice %o A181789 from sympy import sqrt_mod %o A181789 def A181789_gen(): # generator of terms %o A181789 for j in count(9): %o A181789 b = 10**j %o A181789 a = b*10+1 %o A181789 for k in sorted(sqrt_mod(0,a,all_roots=True)): %o A181789 if a*b <= (m:=k**2) < a*(a-1) and len(set(str(m//a))) == 10: %o A181789 yield m %o A181789 A181789_list = list(islice(A181789_gen(),20)) # _Chai Wah Wu_, Mar 23 2024 %Y A181789 Cf. A092118 (biperiod squares), A181790, A181791. %K A181789 nonn,base %O A181789 1,1 %A A181789 _William Rex Marshall_, Nov 12 2010