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A001747 2 together with primes multiplied by 2. 28
2, 4, 6, 10, 14, 22, 26, 34, 38, 46, 58, 62, 74, 82, 86, 94, 106, 118, 122, 134, 142, 146, 158, 166, 178, 194, 202, 206, 214, 218, 226, 254, 262, 274, 278, 298, 302, 314, 326, 334, 346, 358, 362, 382, 386, 394, 398, 422, 446, 454, 458, 466, 478, 482, 502 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

When supplemented with 8, may be considered the "even primes", since these are the even numbers n = 2k which are divisible just by 1, 2, k and 2k. - Louis Zuckerman (louis(AT)trapezoid.com), Sep 12 2000

Sequence gives solutions of sigma(n)-phi(n)=n+tau(n) where tau(n) is the number of divisors of n.

Numbers n such that sigma(n)=3*(n-phi(n)).

Except for 2, orders of non-cyclic groups k (in A060679(n)) such that x^k==1 (mod k) has only 1 solution 2<=x<=k. - Benoit Cloitre, May 10 2002

Numbers n such that A092673(n)=2. - Jon Perry, Mar 02 2004

Except for initial terms, this sequence = A073582 = A074845 = A077017. Starting with the term 10, they are identical. - Robert G. Wilson v, Jun 15 2004

Together with 8 and 16, even numbers n such that n^2 does not divide (n/2)!. - Arkadiusz Wesolowski, Jul 16 2011

Twice noncomposite numbers. - Omar E. Pol, Jan 30 2012

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = A001043(n) - A001223(n+1), except for initial term.

a(n) = A116366(n-2,n-2) for n>2. - Reinhard Zumkeller, Feb 06 2006

A006093(n) = A143201(a(n+1)) for n>1. - Reinhard Zumkeller, Aug 12 2008

a(n) = 2*A008578(n). - Omar E. Pol, Jan 30 2012, and Reinhard Zumkeller, Feb 16 2012

MATHEMATICA

Join[{2}, 2*Prime[Range[60]]] (* Harvey P. Dale, Jul 23 2013 *)

PROG

(PARI) print1(2); forprime(p=2, 97, print1(", "2*p)) \\ Charles R Greathouse IV, Jan 31 2012

CROSSREFS

Cf. A060679, A009530, A098764.

{2} UNION {A100484}.

Sequence in context: A237758 A023499 A103445 * A048670 A239951 A077625

Adjacent sequences:  A001744 A001745 A001746 * A001748 A001749 A001750

KEYWORD

nonn,easy,nice

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified June 29 08:34 EDT 2017. Contains 288859 sequences.