A141164 Numbers having exactly 1 divisor of the form 8*k + 7.

7, 14, 15, 21, 23, 28, 30, 31, 35, 39, 42, 45, 46, 47, 49, 55, 56, 60, 62, 69, 70, 71, 75, 77, 78, 79, 84, 87, 90, 91, 92, 93, 94, 95, 98, 103, 110, 111, 112, 115, 117, 120, 124, 127, 133, 138, 140, 141, 142, 143, 147, 150, 151, 154, 155, 156, 158, 159, 167, 168, 174, 180, 182, 183, 184, 186, 188, 190, 191, 196, 199

Offset: 1

Author

Reinhard Zumkeller, Mar 26 2011

Keywords

• nonn

Examples

			a(1) = A188226(1) = 7.
		

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Numbers having m divisors of the form 8*k + i: A343107 (m=1, i=1), A343108 (m=0, i=3), A343109 (m=0, i=5), A343110 (m=0, i=7), A343111 (m=2, i=1), A343112 (m=1, i=3), A343113 (m=1, i=5), this sequence (m=1, i=7).

Indices of 1 in A188172.

A007522 is a subsequence.

Cf. A004771.

Programs

Haskell

import Data.List (elemIndices)
a141164 n = a141164_list !! (n-1)
a141164_list = map succ $ elemIndices 1 $ map a188172 [1..]

Mathematica

okQ[n_] := Length[Select[Divisors[n] - 7, Mod[#, 8] == 0 &]] == 1; Select[Range[200], okQ]

PARI

res(n, a, b) = sumdiv(n, d, (d%a) == b)
isA141164(n) = (res(n, 8, 7) == 1) \\ Jianing Song, Apr 06 2021

Formula

A188172(a(n)) = 1.