login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A235540 Composite numbers m such that (4^m - 2^m + 8*m^2 - 2) / (2*m*(2*m + 1)) is integral. 3
243, 891, 1539, 2211, 2511, 13203, 19683, 87723, 92583, 150851, 202851, 292923, 321651, 399771, 412623, 452051, 1325843, 1330551, 1441091, 1566891, 3026871, 4422231, 4954851, 4974971, 5016191, 5845851, 5971239, 6773139, 11050911, 11720511, 12602871, 14666751 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Nonprimes in A158034.

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..89

MATHEMATICA

Select[Range[10^6], CompositeQ[#]&&IntegerQ[(4^#-2^#+8#^2-2)/(2#(2#+1))]&] (* Harvey P. Dale, Nov 17 2014 *)

PROG

(Haskell)

a235540 n = a235540_list !! (n-1)

a235540_list = filter ((== 0) . a010051') a158034_list

(Python)

from gmpy2 import is_prime, powmod, t_mod

A235540_list = []

for i in range(1, 10**9+1):

....if not is_prime(i):

........d = 2*i*(2*i+1)

........n = t_mod(powmod(4, i, d)-powmod(2, i, d)+8*i*i-2, d)

........if not n:

............A235540_list.append(i) # Chai Wah Wu, Dec 02 2014

CROSSREFS

Cf. A158034, A010051, A002808.

Sequence in context: A331613 A255626 A205049 * A219132 A232285 A113335

Adjacent sequences:  A235537 A235538 A235539 * A235541 A235542 A235543

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Jan 12 2014

EXTENSIONS

New definition from Reinhard Zumkeller, Nov 17 2014. Thanks to Harvey P. Dale, who observed that the original definition was wrong.

More terms from Harvey P. Dale, Nov 17 2014

More terms from Chai Wah Wu, Dec 02 2014

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 January 27 15:17 EST 2021. Contains 340467 sequences. (Running on oeis4.)