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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.
5
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
OFFSET
1,2
LINKS
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
KEYWORD
nonn,base
AUTHOR
Michel Lagneau, Sep 06 2010
STATUS
approved