login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Please make a donation to keep the OEIS running. In 2017 we replaced the server with a faster one, added 20000 new sequences, and reached 7000 citations (often saying "discovered thanks to the OEIS").
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A055812 a(n) and floor(a(n)/5) are both squares; i.e., squares which remain squares when written in base 5 and last digit is removed. 20
0, 1, 4, 9, 49, 81, 324, 2209, 15129, 25921, 103684, 710649, 4870849, 8346321, 33385284, 228826129, 1568397609, 2687489281, 10749957124, 73681302249, 505019158609, 865363202001, 3461452808004 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

For the first 3 terms, the above "base 5" interpretation is questionable, since they have only 1 digit in base 5. It is understood that dropping this digit yields 0. - M. F. Hasler, Jan 15 2012

LINKS

Table of n, a(n) for n=1..23.

FORMULA

Empirical g.f.: -x^2*(9*x^11 +49*x^10 +324*x^9 +81*x^8 -698*x^7 -698*x^6 -968*x^5 -242*x^4 +49*x^3 +9*x^2 +4*x +1) / ((x -1)*(x +1)*(x^2 -4*x -1)*(x^2 +1)*(x^2 +4*x -1)*(x^4 +18*x^2 +1)). - Colin Barker, Sep 15 2014

EXAMPLE

a(4) = 49 because 49 = 7^2 = 144 base 5 and 14 base 5 = 9 = 3^2.

PROG

(PARI) b=5; for(n=1, 2e9, issquare(n^2\b) && print1(n^2, ", "))  \\ M. F. Hasler, Jan 15 2012

CROSSREFS

For analogs in other bases see A055792 (base 2), A055793 (base 3), A055808 (base 4), A055851 (base 6), A204517 (base 7), A204512 (base 8), A204503 (base 9) and A023110 (base 10).

Squares of A204520. The square roots of floor[a(n)/5] are given in A204521.

Sequence in context: A115711 A029791 A053961 * A268099 A061867 A019544

Adjacent sequences:  A055809 A055810 A055811 * A055813 A055814 A055815

KEYWORD

base,nonn

AUTHOR

Henry Bottomley, Jul 14 2000

EXTENSIONS

More terms added and offset changed to 1 by M. F. Hasler, Jan 15 2012

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 10 05:49 EST 2018. Contains 318044 sequences. (Running on oeis4.)