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

Author

David W. Wilson

Keywords

• nonn

Links

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

Crossrefs

Cf. A074608.

Programs

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 *)