A131771 First differences (A131772) equal this sequence with zeros inserted at positions {m*(m+1)/2, m>=0}.

1, 1, 2, 4, 4, 8, 12, 20, 20, 32, 52, 72, 104, 104, 156, 228, 332, 436, 592, 592, 820, 1152, 1588, 2180, 2772, 3592, 3592, 4744, 6332, 8512, 11284, 14876, 18468, 23212, 23212, 29544, 38056, 49340, 64216, 82684, 105896, 129108, 158652, 158652, 196708

Offset

0,3

Comments

Partial sums yield distinct terms of this sequence.

Links

Table of n, a(n) for n=0..44.

Example

Partial sums (A131770) begin:
[1,2,4,8,12,20,32,52,72,104,156,228,332,436,592,...].
First differences (A131772) begin:
[1,0,1,2,0,4,4,8,0,12,20,20,32,0,52,72,104,104,156,0,228,332,436,592,592,...].

Prog

(PARI) {A131770(n)=if(n<0, 0, if(n==0, 1, A131770(n-1)+A131770(n-(sqrtint(8*n+17)-3)\2)))} {a(n)=A131770(n)-A131770(n-1)}

Crossrefs

Cf. A131770 (partial sums), A131772 (first differences).

Sequence in context: A076342 A135268 A245619 * A335974 A047073 A308528

Adjacent sequences: A131768 A131769 A131770 * A131772 A131773 A131774

Keyword

nonn

Author

Paul D. Hanna, Jul 14 2007

Status

approved