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A237257 Numbers n such that phi(n) = reversal(sigma(n)) - sigma(n). 1
1863, 1979883, 126639495, 162037386, 1979999883, 1061283473946 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

If p = (22*10^k-13)/9 is prime, then 3^4*p is a term of the sequence. This happens for k = 1, 4, 7, 12, 30, 94, 178, 196, 564, ... .

a(7) > 3*10^12.

If k is in the sequence A102953 then p = (22*10^k-13)/9 is prime. 9 divides all known terms, is it true for all terms of this sequence? - Farideh Firoozbakht, Feb 06 2014

LINKS

Table of n, a(n) for n=1..6.

EXAMPLE

n = 1979999883 = 3^4*24444443 is a term, since sigma(n) = 2957777724 and 4277777592 - 2957777724 = 1319999868 = phi(n).

CROSSREFS

Cf. A102953, A230012.

Sequence in context: A132202 A054815 A295995 * A252137 A204889 A204885

Adjacent sequences:  A237254 A237255 A237256 * A237258 A237259 A237260

KEYWORD

nonn,base,more

AUTHOR

Giovanni Resta, Feb 05 2014

STATUS

approved

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Last modified February 19 09:57 EST 2020. Contains 332041 sequences. (Running on oeis4.)