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A173430 Last of consecutive coprime iterations of sum-of-divisors function 1
1, 15, 15, 15, 6, 6, 15, 15, 14, 10, 12, 12, 14, 14, 15, 104, 18, 18, 20, 20, 104, 22, 24, 24, 104, 26, 40, 28, 30, 30, 104, 104, 33, 34, 48, 91, 38, 38, 56, 40, 42, 42, 44, 44, 45, 46, 48, 48, 80, 255, 51, 52, 54, 54, 72, 56, 80, 58, 60, 60, 62, 62, 104, 255, 84, 66, 68, 68 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

Graeme L. Cohen and Herman J. J. te Riele, Iterating the sum-of-divisors function, Experimental Mathematics, 5 (1996), pp. 93-100.

Oystein Ore, Number Theory and Its History, 1988, Dover Publications, ISBN 0486656209, pp. 88-96.

LINKS

Table of n, a(n) for n=1..68.

Leonard Eugene Dickson, History of the Theory of Numbers, Volume I, Divisibility and Primality, Carnegie Institution of Washington, 1919, Chapters II and X

EXAMPLE

Calculating sum-of-divisors ( ... sum-of-divisors ( sum-of-divisors ( 4 ) ) ... ) the iterates are 4, 7, 8, 15, 24, ... .

The initial, consecutive, pairwise, coprime iterates are 4, 7, 8, 15, so a(4) = 15 .

Here sigma ( 4 ) = 7, sigma ( sigma ( 4 ) ) = sigma ( 7 ) = 8, etc.

CROSSREFS

Cf. A129246 and the references there, A019294, A019295, A000203, A051027, A019284, A019277.

Sequence in context: A069785 A290850 A290669 * A010854 A003884 A225917

Adjacent sequences:  A173427 A173428 A173429 * A173431 A173432 A173433

KEYWORD

easy,nonn

AUTHOR

Walter Nissen, Feb 18 2010

STATUS

approved

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Last modified February 23 00:18 EST 2019. Contains 320411 sequences. (Running on oeis4.)