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 A181790 #17 Mar 24 2024 10:49:08 %S A181790 183673469387755102041,326530612244897959184,734693877551020408164, %T A181790 132231404958677685950413223140496,206611570247933884297520661157025, %U A181790 297520661157024793388429752066116,404958677685950413223140495867769 %N A181790 Numbers k such that k concatenated with itself is a pandigital biperiod square. %D A181790 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 A181790 Chai Wah Wu, <a href="/A181790/b181790.txt">Table of n, a(n) for n = 1..34</a> %o A181790 (Python) %o A181790 from itertools import count, islice %o A181790 from sympy import sqrt_mod %o A181790 def A181790_gen(): # generator of terms %o A181790 for j in count(9): %o A181790 b = 10**j %o A181790 a = b*10+1 %o A181790 for k in sorted(sqrt_mod(0,a,all_roots=True)): %o A181790 if a*b <= k**2 < a*(a-1) and len(set(str(m:=k**2//a))) == 10: %o A181790 yield m %o A181790 A181790_list = list(islice(A181790_gen(),20)) # _Chai Wah Wu_, Mar 23 2024 %Y A181790 Cf. A102567, A181789, A181791. %K A181790 nonn,base %O A181790 1,1 %A A181790 _William Rex Marshall_, Nov 12 2010