cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A227027 Triangular numbers representable as x!/y! with y < x-1.

Original entry on oeis.org

6, 120, 210, 990, 7140, 185136, 242556, 2162160, 8239770, 258474216, 279909630, 9508687656, 323015470680, 10973017315470, 372759573255306, 12662852473364940, 430164224521152660, 14612920781245825506, 496409142337836914550
Offset: 1

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Author

Alex Ratushnyak, Jun 27 2013

Keywords

Comments

Triangular numbers in A045619, except A045619(1)=0. The sequence is infinite because A029549 is a subsequence. According to Melissen's comment in A097571, y > x-7.
The sequence of x's producing a(n): A227026.
a(2) and a(3) have two representations:
a(2) = 120 = 5*4*3*2 = 6*5*4.
a(3) = 210 = 7*6*5 = 15*14.

Examples

			990 is in the sequence since 990 = 11!/8! = 11*10*9 is a ratio of factorials and 990 = (44)(44 + 1)/2 is a triangular number.

Crossrefs

Cf. A000217, A001219, A029549, A045619, A097571, A227026.
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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