A190815 A bisection of A049690.

0, 3, 9, 17, 31, 45, 63, 87, 111, 139, 173, 205, 243, 287, 329, 373, 435, 487, 535, 607, 663, 727, 809, 877, 955, 1037, 1117, 1205, 1293, 1385, 1475, 1595, 1695, 1783, 1913, 2005, 2123, 2267, 2379, 2487, 2629, 2763, 2893, 3041, 3177, 3313, 3473, 3625, 3761

Offset: 1

Author

N. J. A. Sloane, May 20 2011

Keywords

• nonn
• easy

Links

• Nathaniel Johnston, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A049690, A099958.

Programs

Magma

[n eq 1 select 0 else (&+[EulerPhi(2*j): j in [1..2*(n-1)]]) : n in [1..60] ]; // G. C. Greubel, Dec 03 2023

Maple

A190815 := proc(n) option remember: if(n=1)then return 0:fi: return procname(n-1)+numtheory[phi](4*n-6)+numtheory[phi](4*n-4): end: seq(A190815(n),n=1..49); # Nathaniel Johnston, May 24 2011

Mathematica

a[n_] := Sum[EulerPhi[2k], {k, 1, 2n-2}];
Table[a[n], {n, 1, 49}] (* Jean-François Alcover, Apr 16 2023 *)

SageMath

[sum(euler_phi(2*j) for j in range(1,2*n-1)) for n in range(1,61)] # G. C. Greubel, Dec 03 2023

Extensions

More terms from Nathaniel Johnston, May 24 2011