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 A068414 Numbers n such that sigma(n) = 3n - 2*phi(n). 4
 1, 12, 56, 260, 992, 1976, 2156, 2754, 16256, 25232, 41072, 133984, 145888, 1100864, 1270208, 1439552, 2237888, 4729664, 67100672, 75398912, 171627376, 277060144, 473089984, 538178048, 558585344, 629225984, 1192258048, 1863840112, 2181070592, 4534854656 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS If 2^p-1 is prime(a Mersenne prime) and n=2^p*(2^p-1) then n is in the sequence because 3*n-2*phi(n)=3*2^p*(2^p-1)-2^p*(2^p-2) =2^p*(2^(p+1)-1)=sigma(2^p-1)*sigma(2^p)=sigma(2^p*(2^p-1))= sigma(n). - Farideh Firoozbakht, Dec 31 2005 LINKS PROG (PARI) for(n=1, 500000, if(sigma(n)==3*n-2*eulerphi(n), print1(n, ", "))) CROSSREFS Cf. A068418, A069719, A069737. Sequence in context: A275505 A009827 A068418 * A199316 A081756 A307741 Adjacent sequences:  A068411 A068412 A068413 * A068415 A068416 A068417 KEYWORD nonn AUTHOR Benoit Cloitre, Mar 03 2002 EXTENSIONS More terms (complete up to 50000000). - Rick L. Shepherd, Mar 28 2002 More terms from Labos Elemer, Apr 03 2002 a(24)-a(30) from Donovan Johnson, Feb 08 2012 STATUS approved

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Last modified January 20 13:06 EST 2022. Contains 350472 sequences. (Running on oeis4.)