A141426 a(n) = A140555(n) - 1.

1, 2, 18, 28, 42, 58, 70, 78, 88, 108, 112, 126, 136, 138, 148, 162, 178, 180, 196, 198, 210, 228, 238, 240, 268, 280, 282, 292, 312, 316, 336, 348, 358, 378, 388, 396, 400, 408, 418, 420, 430, 438, 448, 462, 466, 478, 486, 490, 498, 508, 520, 522, 546, 568

Offset: 1

Author

Giovanni Teofilatto, Aug 06 2008

Keywords

• nonn
• less

Comments

Previous name was: Count of numbers smaller than and coprime to the prime A140555(n).

Crossrefs

Cf. A140555.

Programs

Maple

isA140555 := proc(n) RETURN( isprime(n) and not isprime(n+6) ) ; end: A140555 := proc(n) option remember ; if n = 1 then 2; else for a from procname(n-1)+1 do if isA140555(a) then RETURN(a) ; fi; od: fi; end: A141426 := proc(n) A140555(n)-1 ; end: for n from 1 to 100 do printf("%d,",A141426(n)) ; od: # R. J. Mathar, Aug 12 2008

Mathematica

lim=255;a140555=Select[Prime[Range[lim]], !PrimeQ[#+6]&];a[n_]:=Total[Boole[CoprimeQ[Range[a141426[[n]]-1],a140555[[n]]]]];Array[a,PrimePi[lim]] (* James C. McMahon, Jul 22 2025 *)

Formula

a(n) = phi(A140555(n)) = A140555(n) - 1.

Extensions

Edited and extended by R. J. Mathar, Aug 12 2008

New name from Joerg Arndt, Jul 22 2025