A196127 Union of p-1, 2p-1 and 3p-1 where p is a prime (without repetition).

1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 13, 14, 16, 18, 20, 21, 22, 25, 28, 30, 32, 33, 36, 37, 38, 40, 42, 45, 46, 50, 52, 56, 57, 58, 60, 61, 66, 68, 70, 72, 73, 78, 81, 82, 85, 86, 88, 92, 93, 96, 100, 102, 105, 106, 108, 110, 112, 117, 121, 122, 126, 128, 130

Offset: 1

Author

Juri-Stepan Gerasimov, Sep 28 2011

Keywords

• nonn
• easy

Links

• Nathaniel Johnston, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A006093, A076274.

Programs

Maple

lim:=70: S:={}: p:=1: for n from 1 to lim do p:=nextprime(p): S := S union {p-1,2*p-1,3*p-1}: od: op(1..lim,S); # Nathaniel Johnston, Sep 28 2011

Mathematica

With[{upto=130},Select[{#-1,2#-1,3#-1}&/@Prime[Range[PrimePi[upto]+1]]//Flatten//Union,#<=upto&]] (* Harvey P. Dale, Apr 22 2016 *) (* or *)
Select[Range@130, Or @@ PrimeQ[(#+1)/{1,2,3}] &] (* Giovanni Resta, Apr 30 2019 *)

Extensions

Entries checked by R. J. Mathar, Sep 28 2011