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A001747
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2 together with primes multiplied by 2.
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23
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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; internal format)
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OFFSET
| 1,1
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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
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)!. [From Arkadiusz Wesolowski, Jul 16 2011]
Twice noncomposite numbers. - Omar E. Pol, Jan 30 2012
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LINKS
| T. D. Noe, Table of n, a(n) for n = 1..1000
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FORMULA
| a(n) = A001043(n) - A001223(n+1), except for initial term.
n such that A092673(n)=2 - Jon Perry, Mar 02 2004
a(n) = A116366(n-2,n-2) for n>2. - Reinhard Zumkeller, Feb 06 2006
A006093(n) = A143201(a(n+1)) for n>1. [From Reinhard Zumkeller, Aug 12 2008]
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PROG
| (PARI) print1(2); forprime(p=2, 97, print1(", "2*p)) \\ Charles R Greathouse IV, Jan 31 2012
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CROSSREFS
| Cf. A060679, A009530, A098764.
{2} UNION {A100484}.
Sequence in context: A000065 A023499 A103445 * A048670 A077625 A027383
Adjacent sequences: A001744 A001745 A001746 * A001748 A001749 A001750
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KEYWORD
| nonn,easy,nice
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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