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

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.

Links

Table of n, a(n) for n=1..4.

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 *)

Crossrefs

Cf. A000010, A000203, A004086.

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

Sequence in context: A290741 A261362 A132942 * A131558 A133857 A349519

Adjacent sequences: A237518 A237519 A237520 * A237522 A237523 A237524

Keyword

nonn,base,more

Author

Giovanni Resta, Feb 08 2014

Status

approved