A356398 a(1) = 4, and for any n > 1, a(n+1) is the a(n)-th squarefree number.

4, 5, 6, 7, 10, 14, 21, 33, 53, 85, 138, 222, 366, 599, 985, 1613, 2651, 4357, 7169, 11795, 19401, 31913, 52487, 86347, 142021, 233615, 384277, 632091, 1039741, 1710305, 2813358, 4627790, 7612435, 12521926, 20597674, 33881799, 55733298, 91677666, 150803687

Offset: 1

Author

Rémy Sigrist, Aug 05 2022

Keywords

• nonn

Comments

See A071255 for a similar sequence.

The ratio a(n+1)/a(n) tends to Pi^2/6 (A013661) as n tends to infinity.

Examples

			a(1) = 4 and the fourth squarefree number is 5, so a(2) = 5.
		

Links

• Rémy Sigrist, C program

Crossrefs

Cf. A005117, A006508, A007097, A013661, A071255.

Programs

C

See Links section.

Formula

a(n+1) = A005117(a(n)).