A237257 Numbers k such that phi(k) = reversal(sigma(k)) - sigma(k).

1863, 1979883, 126639495, 162037386, 1979999883, 1061283473946

Offset

1,1

Comments

If p = (22*10^m - 13)/9 is prime, then 3^4*p is a term of the sequence. This happens for m = 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

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

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