A358701 a(n) is the least number > 1 that needs n toggles in the trailing bits of its binary representation to become a square.

4, 5, 7, 14, 79, 831, 6495, 247614, 7361278, 743300286, 121387475838

Offset

0,1

Links

Table of n, a(n) for n=0..10.

Michael S. Branicky, Go program.

Code Golf StackExchange, Toggle some bits and get a square, coding challenge started by user Arnauld, Aug 18 2018.

Delbert L. Johnson, C# program

Example

a(0) = 4 = 100 in binary, 0 toggled bits needed;
a(1) = 5 = 101_2, 1 toggled bit -> 100_2 = 4;
a(2) = 7 = 111_2, 2 toggled bits -> 100_2 = 4;
a(3) = 14 = 1110_2, 3 toggled bits -> 1001_2 = 9;
a(4) = 79 = 1001111_2, 4 toggled bits -> 1000000_2 = 64;
a(5) = 831 = 1100111111_2, 5 toggled bits -> 1100010000_2 = 784 = 28^2.

Prog

See Code Golf link. - Arnauld Chevallier, Aug 18 2018
(Go) // see linked program
(C#) // see linked program

Crossrefs

Cf. A000120, A000290, A001737, A159918.

Sequence in context: A275273 A069575 A250182 * A072215 A106170 A353246

Adjacent sequences: A358698 A358699 A358700 * A358702 A358703 A358704

Keyword

nonn,base,hard,more

Author

Hugo Pfoertner, Dec 16 2022

Extensions

a(9) from Michael S. Branicky, Dec 19 2022

a(10) from Delbert L. Johnson, Apr 13 2024

Status

approved