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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A162887 Odd nonprimes in an alternating 1-based sum up to some odd nonprime.

Original entry on oeis.org

15, 33, 39, 51, 69, 75, 87, 105, 117, 123, 129, 141, 159, 177, 183, 189, 195, 201, 213, 219, 231, 243, 249, 255, 267, 279, 285, 303, 309, 315, 321, 327, 333, 339, 357, 369, 375, 381, 393, 399, 411, 429, 435, 447, 453, 459, 465, 483, 489, 495, 501, 513, 519
Offset: 1

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Author

Juri-Stepan Gerasimov, Jul 16 2009

Keywords

Comments

Define the alternating sum S(u) = sum_{k=0..u} (1-(-1)^k*k) = A064455(u+1) as in A162886.
Evaluate the sum with upper limits u= 1,9, 15, 21... from A014076, and add S(u) to this sequence here whenever it is itself a member of A014076.

Examples

			The sequence S(u) = 3, 15, 24, 33, 39, 42, 51, 54, 60, 69, ... is generated by u = 1, 9, 15, 21, ...
The first S-term, 3, is prime, and therefore not added to the sequence. The second S-term, 15, is an odd nonprime and added to the sequence. The third, 24, is even and not added to the sequence.

Crossrefs

Cf. A014076.

Extensions

3 removed by R. J. Mathar, Aug 27 2009
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