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

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

Author

M. F. Hasler, Dec 28 2013

Keywords

• nonn

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","))