A088040 Smallest fourth power k such that k-1 is divisible by an n-th power, k > 1.

16, 81, 81, 81, 2401, 50625, 923521, 15752961, 260144641, 4228250625, 68184176641, 1095222947841, 17557851463681, 281200199450625, 4501401006735361, 72040003462430721, 1152780773560811521

Offset

1,1

Comments

a(2)=a(3)=a(4) as every odd fourth power is == 1 mod (2^4).

Links

Table of n, a(n) for n=1..17.

Formula

Empirical g.f.: x*(81920*x^7 -75776*x^6 -45184*x^5 +43696*x^4 -2840*x^3 -2530*x^2 +415*x -16) / ((x-1)*(2*x-1)*(4*x-1)*(8*x-1)*(16*x-1)). [Colin Barker, Feb 05 2013]

Example

a(5) = 2401 = 7^4 and 7^4 -1 = (2^5)*3*5^2.
a(6) = 50625 = 15^4 and 15^4 -1 = (2^6)*7*113.

Crossrefs

Cf. A088041.

Sequence in context: A110892 A202880 A339596 * A354799 A359784 A346484

Adjacent sequences: A088037 A088038 A088039 * A088041 A088042 A088043

Keyword

nonn

Author

Amarnath Murthy, Sep 19 2003

Extensions

Corrected and extended by Ray Chandler, Oct 04 2003

Status

approved