cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-1 of 1 results.

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

Original entry on oeis.org

1863, 1979883, 126639495, 162037386, 1979999883, 1061283473946
Offset: 1

Views

Author

Giovanni Resta, Feb 05 2014

Keywords

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

Examples

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

Crossrefs

Cf. A102953, A230012.
Showing 1-1 of 1 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement.