A045586 Numbers k that divide 7^k + 3^k.

1, 2, 5, 25, 55, 58, 125, 155, 275, 605, 625, 775, 1265, 1375, 1682, 1705, 3025, 3125, 3875, 4805, 6325, 6655, 6875, 8525, 13915, 15125, 15625, 18755, 19375, 24025, 29095, 31625, 33275, 34375, 39215, 42625, 48778, 52855, 53882, 69575, 73205

Offset

1,2

Comments

If k is an odd term, then 5*k is a term. - Robert Israel, Oct 10 2025

Links

Amiram Eldar, Table of n, a(n) for n = 1..500

Maple

filter:= t -> 7 &^ t + 3 &^ t mod t = 0:
select(filter, [$1..10^5]); # Robert Israel, Oct 10 2025

Mathematica

Select[Range[75000], Divisible[7^#+3^#, #]&] (* Harvey P. Dale, Apr 21 2019 *)
Select[Range[75000], Divisible[PowerMod[7, #, #] + PowerMod[3, #, #], #] &] (* Amiram Eldar, Oct 23 2021 *)

Crossrefs

Cf. A074608.

Sequence in context: A220170 A273238 A105647 * A137096 A137093 A335213

Adjacent sequences: A045583 A045584 A045585 * A045587 A045588 A045589

Keyword

nonn

Author

David W. Wilson

Status

approved