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 A192287 Quasi-antiperfect numbers. 1
 11, 12, 21, 111, 979, 19521, 279259, 4841411, 7231219, 10238379, 14645479, 136531171, 592994139, 1869506239, 13820158011, 35242846899, 211443753471, 330984643659, 8806335754299 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A quasi-antiperfect number is a least anti-abundant number, i.e., one such that sigma*(n) = n+1, where sigma*(n) is the sum of the anti-divisors of n. Like quasi perfect numbers (see link) but using anti-divisors. a(16) > 2*10^10. - Donovan Johnson, Sep 22 2011 LINKS Eric Weisstein's World of Mathematics, Quasiperfect number EXAMPLE Anti-divisors of 979 are 2, 3, 19, 22, 103, 178, 653. Their sum is 980 and 980 = 979+1. MAPLE P:=proc(n) local a, i, k; for i from 3 to n do a:=0; for k from 2 to i-1 do if abs((i mod k)-k/2)<1 then a:=a+k; fi; od; if i+1=a then print(i); fi; od; end: P(1000000); PROG (PARI) sad(n) = vecsum(select(t->n%t && t

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Last modified March 26 14:32 EDT 2023. Contains 361549 sequences. (Running on oeis4.)