A376509 Natural numbers whose iterated squaring modulo 100 eventually enters the 4-cycle 21, 41, 81, 61.

3, 9, 11, 13, 17, 19, 21, 23, 27, 29, 31, 33, 37, 39, 41, 47, 53, 59, 61, 63, 67, 69, 71, 73, 77, 79, 81, 83, 87, 89, 91, 97, 103, 109, 111, 113, 117, 119, 121, 123, 127, 129, 131, 133, 137, 139, 141, 147, 153, 159, 161, 163, 167, 169, 171, 173, 177, 179, 181

Offset: 1

Author

Martin Renner, Sep 25 2024

Keywords

• nonn

Comments

The natural numbers decompose into six categories under the operation of repeated squaring modulo 100, four of which consist of numbers that eventually settle at the attractors 0 (cf. A008592), 1 (cf. A376506), 25 (cf. A017329), or 76 (cf. A376507), and two of which eventually enter one of the 4-cycles 16, 56, 36, 96 (cf. A376508) or 21, 41, 81, 61 (this sequence).

The first-order differences of the numbers in this sequence repeat with a fixed period of length sixteen: 6, 2, 2, 4, 2, 2, 2, 4, 2, 2, 2, 4, 2, 2, 6, 6, ...

Examples

			3^2 = 9 -> 9^2 = 81 -> 81^2 = 61 -> 61^2 = 21 -> 21^2 = 41 -> 41^2 = 81 -> ... (mod 100)
		

References

• Alexander K. Dewdney, Computer-Kurzweil. Mit einem Computer-Mikroskop untersuchen wir ein Objekt von faszinierender Struktur in der Ebene der komplexen Zahlen. In: Spektrum der Wissenschaft, Oct 1985, p. 8-14, here p. 11-13 (Iterations on a finite set), 14 (Iteration diagram).

Links

• Index entries for linear recurrences with constant coefficients, signature (1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1).

Crossrefs

Cf. A008592, A017329, A376506, A376507, A376508.