

A078923


Possible values of sigma(n)n.


4



0, 1, 3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74
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OFFSET

1,3


COMMENTS

To test whether k>1 is in the sequence, it suffices to check values of n up to (k1)^2, since sigma(n)n >= sqrt(n)+1 if n is composite.


LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..1000


PROG

(PARI) lista(nn) = {for (n=0, nn, if (n==1, kmax=2, kmax=(n1)^2); for (k=1, kmax, if (sigma(k)k == n, print1(n, ", "); break); ); ); } \\ Michel Marcus, Nov 11 2014


CROSSREFS

Cf. A000203, A001065, A002191, A007369. Complement of A005114.
Sequence in context: A317093 A181590 A243293 * A165240 A092460 A092459
Adjacent sequences: A078920 A078921 A078922 * A078924 A078925 A078926


KEYWORD

nonn


AUTHOR

Benoit Cloitre, Dec 15 2002


EXTENSIONS

Edited by Dean Hickerson, Dec 19 2002
Offset fixed by Michel Marcus, Dec 19 2014


STATUS

approved



