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 A319879 #14 Jul 01 2019 12:12:53 %S A319879 1,8,13,18,21,26,29,34,37,40,45,48,51,56,59,62,65,70,73,76,79,84,87, %T A319879 90,93,96,101,104,107,110,113,118,121,124,127,130,133,138,141,144,147, %U A319879 150,153,158,161,164,167,170,173,176,181 %N A319879 a(n) = minimal number m of unit squares needed to make an figure formed from squares (joined edge to edge) which has n holes. %C A319879 The holes must not touch each other. %D A319879 Jean-Paul Delahaye, Des trous à entourer avec parcimonie, Pour las science, No. 501, Juillet 2019, pp. 82-87. %e A319879 Examples from _N. J. A. Sloane_, Jan 30 2019 for n=1, 2, 3: %e A319879 XXX %e A319879 XOX %e A319879 XXX %e A319879 --- %e A319879 XXXXX %e A319879 XOXOX %e A319879 XXXXX %e A319879 ----- %e A319879 XXXXXXX %e A319879 XOXOXOX %e A319879 XXXXXXX %K A319879 nonn %O A319879 0,2 %A A319879 _Jean-Paul Delahaye_, Sep 30 2018 %E A319879 Entry 123 changed to 124 by the author, Jul 01 2019. - _N. J. A. Sloane_, Jul 01 2019