A141426 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

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

LINKS

Table of n, a(n) for n=1..54.

FORMULA

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

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 *)

CROSSREFS

Cf. A140555.

Sequence in context: A366957 A098561 A395348 * A101844 A193598 A190047

Adjacent sequences: A141423 A141424 A141425 * A141427 A141428 A141429

KEYWORD

nonn,less

AUTHOR

Giovanni Teofilatto, Aug 06 2008

EXTENSIONS

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

New name from Joerg Arndt, Jul 22 2025

STATUS

approved