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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A069354 Lowest base with simple divisibility test for n primes; smallest B such that omega(B) + omega(B-1) = n. 2
 2, 3, 6, 15, 66, 210, 715, 7315, 38571, 254541, 728365, 11243155, 58524466, 812646121, 5163068911, 58720148851, 555409903686, 4339149420606 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Indices of record values of primepi(n) - A181834(n) (the number of primes <= n which are not strongly prime to n). - Peter Luschny, Mar 17 2013 As pointed out by Don Reble on the SeqFan list, one has a(n) = A059958(n)+1 at least up to a(18), since so far A001221(m*(m+1)) = n (and not ">") for m = A059958(n). - M. F. Hasler, Jan 15 2014 10^13 < a(19) <= 69322940121436. - Giovanni Resta, Mar 24 2020 LINKS Peter Luschny, Strong coprimality, November 2010. Robert Munafo, Low bases with many divisibility tests FORMULA a(n) = A059958(n) + 1 for 0 < n < 19. - Robert G. Wilson v, Feb 18 2014 EXAMPLE a(4) = 15 because in base 15 you can test for divisibility by 4 different primes (3 and 5 directly, 2 and 7 by "casting out 14's") MAPLE A069354_list := proc(n) local i, L, Max; Max := 1; L := NULL; for i from 2 to n do    if nops(numtheory[factorset](i*(i-1))) = Max    then Max := Max + 1; L := L, i fi; od; L end:  # Peter Luschny, Nov 12 2010 CROSSREFS Cf. A001221, A181834. Sequence in context: A060796 A059842 A001529 * A116632 A214343 A007364 Adjacent sequences:  A069351 A069352 A069353 * A069355 A069356 A069357 KEYWORD nonn,more AUTHOR Robert Munafo, Nov 19 2002 EXTENSIONS More terms added using data from A059958 (see there for credits) by M. F. Hasler, Jan 15 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.

Last modified September 27 04:10 EDT 2021. Contains 347673 sequences. (Running on oeis4.)