A241190 Denominator of Sum_{i=1..n} 1/(prime(i)*prime(i+1)).

6, 30, 42, 462, 6006, 102102, 1939938, 44618574, 1293938646, 40112098026, 1484147626962, 60850052705442, 2616552266334006, 122977956517698282, 6517831695438008946, 7255699434544198638, 442597665507196116918, 29654043588982139833506, 2105437094817731928178926, 153696907921694430757061598

Offset: 1

Author

N. J. A. Sloane, Apr 25 2014, based on a suggestion from Timothy Varghese

Keywords

• nonn
• frac

Comments

a(371) has 1003 decimal digits. - Michael De Vlieger, Jan 27 2016

Examples

			1/6, 7/30, 11/42, 127/462, 1693/6006, 29243/102102, 561623/1939938, 13019431/44618574, 379503437/1293938646, 11809225121/40112098026, 438235268123/1484147626962, ...
		

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..370

Crossrefs

Cf. A024451/A002110, A241189/A241190, A241191/A241192.

Programs

Maple

g:= n-> add(1/(ithprime(i)*ithprime(i+1)),i=1..n);
t1:=[seq(g(n),n=1..20)];
t1a:=map(numer,t1); # A241189
t1b:=map(denom,t1); # A241190

Mathematica

Table[Denominator@ Sum[1/(Prime[i + 1] Prime@ i), {i, n}], {n, 20}] (* Michael De Vlieger, Jan 27 2016 *)

PARI

a(n) = denominator(sum(k=1, n, 1/(prime(k)*prime(k+1)))); \\ Michel Marcus, Jan 27 2016