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A239801 Numbers n such that if x = sigma(n) - n then n = x - phi(x), where phi(n) is the Euler totient function. 1
24, 30, 126, 150, 198, 276, 280, 294, 336, 1644, 3084, 3750, 5720, 13482, 47424, 211884, 11718750, 51028120, 75570560, 88590144 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Fixed points of the transform n -> sigma(n)-n-phi(sigma(n)-n).

LINKS

Table of n, a(n) for n=1..20.

EXAMPLE

sigma(276) = 672 and 672 - 276 = 396; phi(396) = 120 and 396 - 120 = 276.

MAPLE

with(numtheory); P:=proc(q) local n; k:=0;

for n from 1 to q do if 2*n=sigma(n)-phi(sigma(n)-n) then print(n);

fi; od; end: P(10^9);

PROG

(PARI) isok(n) = (x = sigma(n) - n) && (n == x - eulerphi(x)); \\ Michel Marcus, Mar 28 2014

CROSSREFS

Cf. A000010, A000203, A239802.

Sequence in context: A135045 A109321 A067952 * A123200 A167307 A161378

Adjacent sequences:  A239798 A239799 A239800 * A239802 A239803 A239804

KEYWORD

nonn,more

AUTHOR

Paolo P. Lava, Mar 27 2014

EXTENSIONS

a(17)-a(20) from Michel Marcus, Mar 28 2014

STATUS

approved

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Last modified April 19 18:37 EDT 2019. Contains 322290 sequences. (Running on oeis4.)