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A237521
Numbers k such that phi(k) + sigma(k) = reversal(k) + 2.
4
2, 22605, 26026, 492775589
OFFSET
1,1
COMMENTS
a(5), if it exists, is larger than 10^13.
Up to 10^13 the equation phi(k) + sigma(k) = reversal(k) - 2 is satisfied only by k = 26330276.
EXAMPLE
22605 is in the sequence because phi(22605) = 10880, sigma(22605) = 39744, and 10880 + 39744 = 50622 + 2, where 50622 is the reversal of 22605.
MATHEMATICA
Select[Range[493*10^6], EulerPhi[#]+DivisorSigma[1, #]== IntegerReverse[ #]+2&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jan 01 2020 *)
KEYWORD
nonn,base,more
AUTHOR
Giovanni Resta, Feb 08 2014
STATUS
approved