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A180272 a(n) = binomial(n, A002024(n+1)-1) where A002024 is "n appears n times". 1
1, 1, 2, 3, 6, 10, 20, 35, 56, 84, 210, 330, 495, 715, 1001, 3003, 4368, 6188, 8568, 11628, 15504, 54264, 74613, 100947, 134596, 177100, 230230, 296010, 1184040, 1560780, 2035800, 2629575, 3365856, 4272048, 5379616, 6724520, 30260340 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Paul D. Hanna, Table of n, a(n) for n = 0..1000

EXAMPLE

G.f.: A(x) = 1 + x + 2*x^2 + 3*x^3 + 6*x^4 + 10*x^5 + 20*x^6 +...

Terms are shown below in parenthesis as they appear in Pascals triangle:

(1);

1,(1);

1,(2),1;

1,3,(3),1;

1,4,(6),4,1;

1,5,(10),5,1;

1,6,15,(20),15,6,1;

1,7,21,(35),35,21,7,1;

1,8,28,(56),70,56,28,8,1;

1,9,36,(84),126,126,84,36,9,1;

1,10,45,120,(210),252,210,120,45,10,1; ...

PROG

(PARI) {a(n)=binomial(n, (sqrtint(8*n+1)-1)\2)}

CROSSREFS

Cf. A002024.

Sequence in context: A077027 A030436 A030227 * A319436 A061551 A026034

Adjacent sequences:  A180269 A180270 A180271 * A180273 A180274 A180275

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Jan 17 2011

STATUS

approved

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Last modified November 18 19:59 EST 2019. Contains 329288 sequences. (Running on oeis4.)