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A077064 Squarefree numbers of form prime - 1. 7
1, 2, 6, 10, 22, 30, 42, 46, 58, 66, 70, 78, 82, 102, 106, 130, 138, 166, 178, 190, 210, 222, 226, 238, 262, 282, 310, 330, 346, 358, 366, 382, 418, 430, 438, 442, 462, 466, 478, 498, 502, 546, 562, 570, 586, 598, 606, 618, 642, 646, 658, 682, 690, 718, 742 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A077063(a(n)) = a(n).

Also, squarefree totients of numbers divisible by an even number of primes. - Torlach Rush, Dec 22 2017

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..10000

FORMULA

0 <> mu(phi(1=mu(m))) 0 < m. - Torlach Rush, Dec 22 2017

EXAMPLE

A005117(44)=70=2*5*7 is a term as 70=A000040(20)-1=71-1.

MATHEMATICA

Select[Prime[Range[200]]-1, SquareFreeQ] (* Harvey P. Dale, Feb 09 2015 *)

PROG

(PARI) isok(n) = issquarefree(n) && isprime(n+1); \\ Michel Marcus, Mar 22 2016

(PARI) lista(nn) = forprime(p=2, nn, if (issquarefree(p-1), print1(p-1, ", "))); \\ Michel Marcus, Mar 22 2016

CROSSREFS

Cf. A006093, A005117, A000040, A077067.

Sequence in context: A180230 A186296 A140775 * A080715 A034168 A055745

Adjacent sequences:  A077061 A077062 A077063 * A077065 A077066 A077067

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Oct 23 2002

STATUS

approved

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Last modified January 25 01:49 EST 2020. Contains 331229 sequences. (Running on oeis4.)