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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A234640 Odd numbers n for which sigma(sigma(sigma(n))) is odd.

Original entry on oeis.org

1, 25, 29, 99, 125, 137, 243, 279, 281, 309, 317, 343, 361, 373, 461, 509, 519, 585, 603, 641, 693, 703, 709, 725, 747, 783, 807, 809, 875, 883, 895, 905, 929, 933, 979, 995, 1003, 1007, 1043, 1059, 1091, 1121, 1133, 1323, 1591, 1597, 1701, 1707, 1779, 1801, 1895, 1973
Offset: 1

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Author

M. F. Hasler, Dec 28 2013

Keywords

Comments

Also, odd numbers such that sigma(sigma(n)) is in A028982.
Subsequence of odd terms of A234639. See also A234638, and A234641 with further cross references.

Programs

  • PARI
    forstep(n=1,1999,2,sigma(sigma(sigma(n)))%2 && print1(n","))
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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