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A178601
a(n) = s(s(n)), where s(n) = sigma(n)-n = A001065(n).
1
0, 0, 1, 0, 6, 0, 1, 3, 7, 0, 15, 0, 8, 4, 9, 0, 11, 0, 14, 1, 10, 0, 55, 6, 15, 1, 28, 0, 54, 0, 1, 9, 22, 1, 17, 0, 14, 1, 43, 0, 66, 0, 50, 15, 16, 0, 64, 7, 1, 11, 26, 0, 78, 1, 63, 1, 31, 0, 172, 0, 20, 1, 41, 1, 90, 0, 32, 13, 40, 0, 45, 0, 50, 8, 63, 1, 144, 0, 56, 50, 40, 0, 196, 1, 26, 15, 76, 0, 259, 11, 64, 13, 43, 6, 236, 0
OFFSET
2,5
LINKS
Carl Pomerance, The first function and its iterates, pp. 125-138 in Connections in Discrete Mathematics, ed. S. Butler et al., Cambridge, 2018.
MATHEMATICA
Table[Apply[ Plus, Divisors[Apply[ Plus, Divisors[n]] - n]] - (Apply[Plus, Divisors[n]] - n), {n, 0, 100}]
PROG
(PARI)
A001065(n) = (sigma(n) - n);
A178601(n) = A001065(A001065(n)); \\ Antti Karttunen, Nov 01 2017
CROSSREFS
Cf. A206708 (fixed points, union of A000396 and A063990). - Antti Karttunen, Nov 01 2017
Sequence in context: A020796 A011253 A049248 * A094691 A095715 A321215
KEYWORD
nonn
AUTHOR
Roger L. Bagula, May 30 2010
EXTENSIONS
Edited by N. J. A. Sloane, May 30 2010
Terms a(0) and a(1) removed and more terms added by Antti Karttunen, Nov 01 2017
STATUS
approved