A167394 Largest single or isolated prime < n-th single or isolated composite.

2, 2, 2, 2, 23, 37, 53, 67, 97, 97, 131, 131, 173, 173, 173, 223, 233, 263, 277, 307, 337, 409, 409, 457, 509, 563, 593, 613, 631, 653, 797, 797, 797, 853, 877, 1013, 1013, 1039, 1039, 1087, 1129, 1223, 1259, 1283, 1297, 1307, 1423, 1447, 1471, 1471, 1601, 1613

Offset

1,1

Links

Table of n, a(n) for n=1..52.

Maple

isA007510 := proc(n) isprime(n) and not isprime(n+2) and not isprime(n-2) ; simplify(%) ; end proc:
A167394 := proc(n) local a; for a from A014574(n)-1 by -1 do if isA007510(a) then return a; end if; end do: end proc:
seq(A167394(n), n=1..120) ; # R. J. Mathar, May 30 2010

Crossrefs

Cf. A007510, A014574.

Sequence in context: A067096 A259704 A249779 * A029627 A075182 A292023

Adjacent sequences: A167391 A167392 A167393 * A167395 A167396 A167397

Keyword

nonn

Author

Juri-Stepan Gerasimov, Nov 02 2009

Extensions

Corrected (47 replaced with 53, 211 replaced with 223, etc.) by R. J. Mathar, May 30 2010

Status

approved