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.

1, 8, 13, 18, 21, 26, 29, 34, 37, 40, 45, 48, 51, 56, 59, 62, 65, 70, 73, 76, 79, 84, 87, 90, 93, 96, 101, 104, 107, 110, 113, 118, 121, 124, 127, 130, 133, 138, 141, 144, 147, 150, 153, 158, 161, 164, 167, 170, 173, 176, 181

Offset: 0

Author

Jean-Paul Delahaye, Sep 30 2018

Keywords

• nonn

Comments

The holes must not touch each other.

Examples

			Examples from _N. J. A. Sloane_, Jan 30 2019 for n=1, 2, 3:
XXX
XOX
XXX
---
XXXXX
XOXOX
XXXXX
-----
XXXXXXX
XOXOXOX
XXXXXXX
		

References

• Jean-Paul Delahaye, Des trous à entourer avec parcimonie, Pour las science, No. 501, Juillet 2019, pp. 82-87.

Extensions

Entry 123 changed to 124 by the author, Jul 01 2019. - N. J. A. Sloane, Jul 01 2019