A176657 Numbers k such that prime(k) is not a twin prime and prime(prime(k)) is a twin prime.

1, 16, 23, 24, 30, 40, 55, 56, 59, 63, 68, 71, 74, 80, 87, 93, 95, 103, 106, 107, 108, 112, 118, 122, 126, 128, 129, 132, 136, 137, 150, 159, 169, 187, 188, 193, 199, 244, 248, 258, 267, 271, 276, 281, 284, 285, 292, 299, 300, 304, 310, 311, 312, 317, 325, 327

Offset

1,2

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

1 is a term because prime(1) = 2 is not a twin prime and prime(prime(1)) = 3 is a twin prime.

Maple

A006450 := proc(n) ithprime(ithprime(n)) ; end proc: isA176657 := proc(n) isA007510(ithprime(n)) and not isA007510(A006450(n)) ; end proc: for n from 1 to 1600 do if isA176657(n) then printf("%d, ", n) ; end if; end do: # R. J. Mathar, Apr 26 2010

Mathematica

A006450[n_] := Prime[Prime[n]];
isA007510[n_] := !PrimeQ[n-2] && !PrimeQ[n+2];
isA176657[n_] := isA007510[Prime[n]] && !isA007510[A006450[n]];
Reap[For[n = 1, n <= 1000, n++, If[isA176657[n], Sow[n]]]][[2, 1]] (* Jean-François Alcover, Oct 15 2020, after Maple *)

Crossrefs

Cf. A006450, A007510.

Sequence in context: A306163 A317380 A070572 * A006616 A225929 A179370

Adjacent sequences: A176654 A176655 A176656 * A176658 A176659 A176660

Keyword

nonn

Author

Juri-Stepan Gerasimov, Apr 23 2010

Extensions

Corrected (29 removed, 126 inserted, 202 removed) and extended by R. J. Mathar, Apr 26 2010

Status

approved