The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A129316 Positive integers k such that sopfr(k) divides sopfr(k+1), where sopfr(k) is the sum of the prime factors of k, counting multiplicity. 5
 5, 8, 15, 77, 125, 160, 252, 496, 714, 948, 980, 1045, 1053, 1260, 1330, 1378, 1404, 1430, 1508, 1520, 1610, 1750, 1862, 1890, 2170, 2491, 2680, 2821, 3094, 3100, 3248, 3400, 3591, 3610, 3652, 3808, 4185, 4191, 4384, 4452, 4500, 4598, 4906, 5120, 5145 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A generalization of Ruth-Aaron pairs (A006145). LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harvey P. Dale) FORMULA sopfr(k+1) mod sopfr(k) = 0. EXAMPLE a(6)=160 since sopfr(160)=sopfr(2^5*5)=10+5=15 and sopfr(161)=sopfr(7*23)=30. MATHEMATICA sopf[n_]:=Total[Flatten[Table[#[[1]], {#[[2]]}]&/@FactorInteger[n]]]; Rest[ Flatten[Position[Partition[Table[sopf[n], {n, 5200}], 2, 1], _?(Divisible[#[[2]], #[[1]]]&), {1}, Heads->False]]] (* Harvey P. Dale, Jul 18 2013 *) CROSSREFS Cf. A001414, A006145, A039752, A129317, A129318, A129319. Sequence in context: A259585 A220034 A063731 * A039752 A141536 A314561 Adjacent sequences:  A129313 A129314 A129315 * A129317 A129318 A129319 KEYWORD easy,nonn AUTHOR Walter Kehowski, Apr 09 2007 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified February 27 12:22 EST 2020. Contains 332306 sequences. (Running on oeis4.)