

A252477


Integer part of 1/(sqrt(prime(n+1))sqrt(prime(n))).


2



3, 1, 2, 1, 3, 1, 4, 2, 1, 5, 1, 3, 6, 3, 2, 2, 7, 2, 4, 8, 2, 4, 3, 2, 4, 10, 5, 10, 5, 1, 5, 3, 11, 2, 12, 4, 4, 6, 4, 4, 13, 2, 13, 6, 14, 2, 2, 7, 15, 7, 5, 15, 3, 5, 5, 5, 16, 5, 8, 16, 3, 2, 8, 17, 8, 2, 6, 3, 18, 9, 6, 4, 6, 6, 9, 6, 4, 9, 5, 4, 20, 4, 20, 6, 10, 7, 5, 10, 21, 10, 3, 5
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,1


COMMENTS

Andrica's conjecture states that sqrt(prime(n+1))sqrt(prime(n)) < 1 for all n. Since equality cannot happen, this is equivalent to say that all terms of is sequence are >= 1.
Sequence A074976 is based on the same idea (rounding to the nearest integer instead).
It is a remarkable coincidence(?) that very often, especially around "peaks", a symmetric pattern "x, y, x" occurs: 2, 7, 2,... 10, 5, 10,... 13, 2, 13,... 20, 4, 20, ..., 11, 5, 11, ...
Equal to the integer part of (A000006(n+1)+A000006(n))/(prime(n+1)prime(n)) for most indices; exceptions are 1, 129, 1667, 2004, 2088, 2334, 3377, 3585, 3695, 3834, 4978, 7057, 7950, 8103, 9525, 9805,...


LINKS

M. F. Hasler, Table of n, a(n) for n = 1..10000
Eric Weisstein's World of Mathematics, Andrica's conjecture


EXAMPLE

a(1) = floor(1/(sqrt(3)  sqrt(2))) = floor(1/(1.731.41)) = floor(1/0.32) = floor(3.15) = 3.
a(2) = floor(1/(sqrt(5)  sqrt(3))) = floor(1/(2.2361.732)) = floor(1/0.504) = floor(1.98) = 1.


PROG

(PARI) a(n)=1\(sqrt(prime(n+1))sqrt(prime(n))) \\ M. F. Hasler, Dec 31 2014
(Haskell)
a252477 n = a252477_list !! (n1)
a252477_list = map (floor . recip) $ zipWith () (tail rs) rs
where rs = map (sqrt . fromIntegral) a000040_list
 Reinhard Zumkeller, Jan 04 2015


CROSSREFS

Cf. A000040, A074976.
Sequence in context: A030777 A056595 A160097 * A029351 A178638 A290496
Adjacent sequences: A252474 A252475 A252476 * A252478 A252479 A252480


KEYWORD

nonn


AUTHOR

M. F. Hasler, Dec 31 2014


STATUS

approved



