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
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
a(19)-a(21) from Michael S. Branicky, Feb 11 2023
a(22) from Michael S. Branicky, Feb 23 2023
STATUS
approved