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A171256 Numbers n such that sigma(n) = 10*phi(n) (where sigma=A000203, phi=A000010). 5
168, 270, 570, 2376, 2436, 5016, 6426, 7110, 13566, 15834, 34452, 58520, 62568, 72732, 75210, 113832, 126882, 168756, 169218, 191862, 199368, 223938, 240312, 280488, 308568, 321468, 420888, 449442, 472758, 661848, 673608, 776736, 848540, 854496, 907236 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

If n is in this sequence, then for any prime p not dividing n, sigma(np) - 10*phi(np) = 2*sigma(n).

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..1000

Kevin A. Broughan and Daniel Delbourgo, On the Ratio of the Sum of Divisors and Euler’s Totient Function I, Journal of Integer Sequences, Vol. 16 (2013), Article 13.8.8.

Kevin A. Broughan and Qizhi Zhou, On the Ratio of the Sum of Divisors and Euler's Totient Function II, Journal of Integer Sequences, Vol. 17 (2014), Article 14.9.2.

PROG

(PARI) for(k=1, 10^6, sigma(k) - 10*eulerphi(k) | print1(k", "));

CROSSREFS

Cf. A062699, A068391, A068390, A136547, A104900, A136540, A104901, A163667, A171257, A104902, A171258, A171259, A171260, A104903.

Sequence in context: A117529 A196591 A060662 * A059463 A302365 A038812

Adjacent sequences:  A171253 A171254 A171255 * A171257 A171258 A171259

KEYWORD

nonn

AUTHOR

M. F. Hasler, Mar 19 2010

STATUS

approved

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Last modified November 15 08:58 EST 2019. Contains 329144 sequences. (Running on oeis4.)