

A109798


Second of a pair of compatible numbers, where two numbers m and n are compatible if sigma(n)2dn=sigma(m)2dm=m+n, for some proper divisors dn and dm of m and n respectively.


0



28, 40, 42, 52, 60, 96, 102, 104, 124, 110, 182, 182, 188, 210, 230, 234, 184, 358, 362, 204, 312, 248, 252, 408, 372, 424, 306, 388, 418, 434, 376, 516, 384, 508, 530, 638, 782, 572, 888, 782, 828, 872, 592, 644, 820, 650, 938, 908, 1026, 1034, 1102, 976, 760
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OFFSET

1,1


LINKS

Table of n, a(n) for n=1..53.
T. Trotter, Admirable Numbers. [Warning: As of March 2018 this site appears to have been hacked. Proceed with great caution. The original content should be retrieved from the Wayback machine and added here.  N. J. A. Sloane, Mar 29 2018]


EXAMPLE

sigma(42)2(1)=962=94 and sigma(52)2(2)=984=94 and 42+52=94 so a(4)=52.


MAPLE

L:=remove(proc(z) isprime(z) end, [$1..10000]): S:=proc(n) map(proc(z) sigma(n) 2*z end, divisors(n) minus {n}) end; CK:=map(proc(z) [z, S(z)] end, L): CL:=[]: for j from 1 to nops(CK)1 do x:=CK[j, 1]; sx:=sigma(x); Sx:=CK[j, 2]; for k from j+1 to nops(CK) while CK[k, 1]<sx do y:=CK[k, 1]; if x+y in Sx intersect CK[k, 2] then CL:=[op(CL), [x, y, x+y]] fi od od;


CROSSREFS

Cf. A111592.
Sequence in context: A179166 A034964 A195897 * A216594 A084807 A184032
Adjacent sequences: A109795 A109796 A109797 * A109799 A109800 A109801


KEYWORD

nonn


AUTHOR

Walter Kehowski, Aug 15 2005


STATUS

approved



