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 A133814 Smallest primitive abundant number or perfect number with 2^n as a factor. 0
 945, 6, 20, 88, 272, 1184, 4288, 16768, 65792, 266752, 1055744, 4204544, 16789504, 67248128, 268877824, 1073840128, 4295032832, 17183670272, 68720263168, 274888916992, 1099518967808, 4398082162688, 17592248958976 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS For n>=1, a(n) = 2^n*A014210(n). - Michel Marcus, Mar 07 2013 LINKS EXAMPLE 945=3^3*5*7 least primitive abundant number with no factor 2, a(0)=945 6=2*3 perfect number, a(1)=6 20=2^2*5 primitive abundant number < 28=2^2*7 perfect number, a(2)=20 88=2^3*11 272=2^4*17 1184=2^5*37 4288=2^6*67 16768=2^7*131 65792=2^8*257 266752=2^9*521 PROG (PARI) isprab(v) = {sig = sigma(v); if (sig < 2*v, return (0)); if (sig == 2*v, return (1)); fordiv (v, d, if ((d != v) && (sigma(d)>=2*d), return (0)); ); return (1); } a(n) = {p = 2^n; k = 3; while (1, v = p * k; if (isprab(v), return (v)); k += 2; ); \\Michel Marcus, Mar 07 2013 CROSSREFS Sequence in context: A145493 A271765 A343330 * A104438 A125013 A294576 Adjacent sequences:  A133811 A133812 A133813 * A133815 A133816 A133817 KEYWORD nonn AUTHOR Pierre CAMI, Jan 06 2008 EXTENSIONS More terms from Michel Marcus, Mar 07 2013 STATUS approved

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Last modified December 6 04:20 EST 2021. Contains 349562 sequences. (Running on oeis4.)