A354418 a(n) is the denominator of the sum of the reciprocals of the first n squarefree numbers.

1, 2, 6, 30, 5, 35, 70, 770, 10010, 5005, 15015, 255255, 4849845, 1616615, 3233230, 74364290, 37182145, 1078282205, 6469693230, 200560490130, 6077590610, 3038795305, 607759061, 22487085257, 44974170514, 134922511542, 5531822973222, 921970495537, 39644731308091

Offset: 1

Author

Ilya Gutkovskiy, May 26 2022

Keywords

• nonn
• frac

Examples

			1, 3/2, 11/6, 61/30, 11/5, 82/35, 171/70, 1951/770, 26133/10010, 13424/5005, 41273/15015, ...
		

Crossrefs

Cf. A002110, A002805, A005117, A034386, A051451, A072983, A354417 (numerators).

Programs

Mathematica

Accumulate[1/Select[Range[43], SquareFreeQ]] // Denominator

PARI

a(n) = my(i=0, s=0); for(x=1, oo, if(core(x)==x, s+=1/x; i++; if(i==n, return(denominator(s))))) \\ Felix Fröhlich, May 26 2022