A132801 a(0)=1; a(n) = Sum_{1<=k<=n, gcd(k,n)=1} a(floor(k/2)), where the sum is over those positive integers which are <= n and are coprime to n.

1, 1, 1, 2, 2, 4, 2, 7, 5, 8, 6, 17, 8, 23, 11, 20, 20, 44, 15, 57, 25, 40, 35, 94, 40, 101, 62, 114, 79, 184, 50, 215, 118, 155, 133, 247, 123, 378, 189, 311, 194, 532, 117, 597, 295, 373, 337, 801, 297, 825, 393, 741, 530, 1239, 399, 1088, 673, 1042, 833, 1871, 530

Offset

0,4

Links

Table of n, a(n) for n=0..60.

Example

The positive integers which are <= 12 and are coprime to 12 are 1,5,7,11. Dividing each of these by 2 and rounding down, we get 0,2,3,5. So a(12) = a(0) + a(2) + a(3) + a(5) = 1+1+2+4 = 8.

Mathematica

a = {1}; For[n = 1, n < 70, n++, s = 0; b = Select[Range[n], GCD[n, # ] == 1 &]; For[j = 1, j < Length[b] + 1, j++, s = s + a[[Floor[b[[j]]/2] + 1]]]; AppendTo[a, s]]; a (* Stefan Steinerberger, Nov 20 2007 *)

Crossrefs

Sequence in context: A359102 A003980 A286369 * A321199 A324604 A270366

Adjacent sequences: A132798 A132799 A132800 * A132802 A132803 A132804

Keyword

nonn

Author

Leroy Quet, Nov 17 2007

Extensions

More terms from Stefan Steinerberger, Nov 20 2007

Status

approved