OFFSET
1,1
COMMENTS
No further terms up to 10^6.
a(7) > 10^10. - Hiroaki Yamanouchi, Mar 18 2015
LINKS
Diana Mecum, Anti-divisors from 3 to 500
EXAMPLE
Antidivisors of 20 are 3,8,13 and their sum is 24, while sigma(20) = 42.
Antidivisors of 26 are 3,4,17 and their sum is 24, while sigma(26) = 42.
Antidivisors of 36531 are 2, 6, 18, 22, 54, 66, 82, 162, 198, 246, 594, 738, 902, 1782, 2214, 2706, 6642, 8118, 24354 and their sum is sigma*(36531) = 48906, while sigma(36531) = 60984.
MAPLE
with(numtheory):T:=proc(w) local x, y, z; y:=w; z:=0;
for x from 1 to ilog10(w)+1 do z:=10*z+(y mod 10); y:=trunc(y/10); od; z; end:
P:=proc(q) local a, j, k, n; for n from 1 to q do
k:=0; j:=n; while j mod 2 <> 1 do k:=k+1; j:=j/2; od;
a:=sigma(2*n+1)+sigma(2*n-1)+sigma(n/2^k)*2^(k+1)-6*n-2;
if T(a)=sigma(n) then print(n); fi; od; end: P(10^10);
PROG
(PARI) rev(n) = subst(Polrev(digits(n)), x, 10);
sad(n) = k=valuation(n, 2); sigma(2*n+1)+sigma(2*n-1)+sigma(n/2^k)*2^(k+1)-6*n-2;
isok(n) = sigma(n) == rev(sad(n)); \\ Michel Marcus, Dec 07 2014
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Paolo P. Lava, Oct 14 2014
EXTENSIONS
a(5) from Chai Wah Wu, Dec 06 2014
a(6) from Hiroaki Yamanouchi, Mar 18 2015
STATUS
approved