A175795 - OEIS

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A175795

Numbers n such that the digits of sigma(n) are exactly the same (albeit in different order) as the digits of phi(n), in base 10.

1, 65, 207, 1769, 2066, 2771, 3197, 4330, 4587, 4769, 4946, 5067, 6443, 6623, 6989, 7133, 8201, 9263, 11951, 12331, 13243, 16403, 17429, 17441, 21416, 22083, 23161, 24746, 27058, 27945, 28049, 28185, 28451, 29111, 30551, 31439, 32554, 32566, 32849, 33715

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OFFSET

1,2

LINKS

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

EXAMPLE

2771 is in the sequence because sigma(2771) = 2952, phi(2771) = 2592

MATHEMATICA

okQ[n_] := Module[{idn = IntegerDigits[DivisorSigma[1, n]]}, Sort[idn] == Sort[IntegerDigits[EulerPhi[n]]]]; Select[Range[40000], okQ]

PROG

(Python)

from sympy import totient, divisor_sigma

A175795_list = [n for n in range(1, 10**4) if sorted(str(divisor_sigma(n))) == sorted(str(totient(n)))] # Chai Wah Wu, Dec 13 2015

(PARI) isok(n) = (de = digits(eulerphi(n))) && (ds = digits(sigma(n))) && (vecsort(de) == vecsort(ds)); \\ Michel Marcus, Dec 13 2015

CROSSREFS

Cf. A000010 (Euler totient function), A000203 (sigma function), A115920, A115921, A114065.

Sequence in context: A051968 A242318 A200867 * A056777 A048512 A237039

Adjacent sequences: A175792 A175793 A175794 * A175796 A175797 A175798

KEYWORD

nonn,base

AUTHOR

Michel Lagneau, Sep 06 2010

STATUS

approved