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!)
A083734 Pseudoprimes to bases 3 and 5. 2
1541, 1729, 1891, 2821, 6601, 8911, 15841, 29341, 41041, 46657, 52633, 63973, 75361, 88831, 101101, 112141, 115921, 126217, 146611, 162401, 172081, 188461, 218791, 252601, 294409, 314821, 334153, 340561, 342271, 399001, 410041, 416641 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..15806 (terms 1..147 from R. J. Mathar)

F. Richman, Primality testing with Fermat's little theorem

FORMULA

a(n) = n-th positive integer k(>1) such that 3^(k-1) = 1 (mod k) and 5^(k-1) = 1 (mod k).

EXAMPLE

a(1)=1541 since it is the first nonprime number such that 3^(k-1) = 1 (mod k) and 5^(k-1) = 1 (mod k). - clarified by Harvey P. Dale, Jan 29 2013

MATHEMATICA

Select[Range[420000], !PrimeQ[#]&&PowerMod[3, #-1, #]==PowerMod[5, #-1, #]==1&] (* Harvey P. Dale, Jan 29 2013 *)

CROSSREFS

Intersection of A005935 and A005936.

Sequence in context: A200429 A092717 A203134 * A137598 A252966 A133560

Adjacent sequences:  A083731 A083732 A083733 * A083735 A083736 A083737

KEYWORD

easy,nonn

AUTHOR

Serhat Sevki Dincer (sevki(AT)ug.bilkent.edu.tr), May 05 2003

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 February 23 12:38 EST 2020. Contains 332159 sequences. (Running on oeis4.)