A237521 Numbers k such that phi(k) + sigma(k) = reversal(k) + 2.

2, 22605, 26026, 492775589

Offset: 1

Author

Giovanni Resta, Feb 08 2014

Keywords

• nonn
• base
• more

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.

Examples

			22605 is in the sequence because phi(22605) = 10880, sigma(22605) = 39744, and 10880 + 39744 = 50622 + 2, where 50622 is the reversal of 22605.
		

Crossrefs

Cf. A000010, A000203, A004086.

Cf. A070272, A230004, A230005, A230006, A230019, A136544, A237522.

Programs

Mathematica

Select[Range[493*10^6],EulerPhi[#]+DivisorSigma[1,#]== IntegerReverse[ #]+2&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jan 01 2020 *)