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A237521 Numbers n such that phi(n) + sigma(n) = reversal(n) + 2. 4
2, 22605, 26026, 492775589 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(5), if it exists, is larger than 10^13.

Up to 10^13 the equation phi(n) + sigma(n) = reversal(n) - 2 is satisfied only by n = 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. A070272, A230004, A230005, A230006, A230019, A136544, A237522.

Sequence in context: A290741 A261362 A132942 * A131558 A133857 A232869

Adjacent sequences:  A237518 A237519 A237520 * A237522 A237523 A237524

KEYWORD

nonn,base,more

AUTHOR

Giovanni Resta, Feb 08 2014

STATUS

approved

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Last modified January 26 20:11 EST 2020. Contains 331288 sequences. (Running on oeis4.)