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A131771 First differences (A131772) equal this sequence with zeros inserted at positions {m*(m+1)/2, m>=0}. 4
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 (list; graph; refs; listen; history; text; internal format)
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 * A047073 A069753 A181245

Adjacent sequences:  A131768 A131769 A131770 * A131772 A131773 A131774

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Jul 14 2007

STATUS

approved

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Last modified October 21 04:10 EDT 2018. Contains 316405 sequences. (Running on oeis4.)