

A157049


a(n) = the largest integer < p(n+1) that is coprime to (p(n+1)p(n)), where p(n) is the nth prime.


2



2, 3, 5, 9, 11, 15, 17, 21, 25, 29, 35, 39, 41, 45, 49, 55, 59, 65, 69, 71, 77, 81, 85, 95, 99, 101, 105, 107, 111, 125, 129, 133, 137, 147, 149, 155, 161, 165, 169, 175, 179, 189, 191, 195, 197, 209, 221, 225, 227, 231, 235, 239, 249, 253, 259, 265, 269, 275, 279
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OFFSET

1,1


COMMENTS

A157048(n)  A157049(n) = 1,2,4,8,10,14,16,20,24,28,34,38,40,44,48,54,..., ; a strictly monotonically increasing sequence.  Robert G. Wilson v, Apr 08 2009


LINKS

Jens Kruse Andersen, Table of n, a(n) for n = 1..10000


EXAMPLE

The 11th prime is 31. The 12th prime is 37. 3731 = 6. The largest integer < 37 that is coprime to 6 is 35, which is a(11).


MATHEMATICA

f[n_] := Block[{k, p = Prime@n, q = Prime[n + 1]}, k = q  1; While[ GCD[q  p, k] > 1, k ]; k]; Array[f, 59] (* Robert G. Wilson v, Apr 08 2009 *)


PROG

(PARI) a(n) = d=prime(n+1)prime(n); k=prime(n+1)1; while(gcd(k, d)>1, k); k \\ Jens Kruse Andersen, Jul 31 2014


CROSSREFS

Cf. A157048, A001223.
Sequence in context: A014109 A328642 A102940 * A195668 A324698 A059042
Adjacent sequences: A157046 A157047 A157048 * A157050 A157051 A157052


KEYWORD

nonn


AUTHOR

Leroy Quet, Feb 22 2009


EXTENSIONS

More terms from Robert G. Wilson v, Apr 08 2009


STATUS

approved



