

A109797


First 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



24, 30, 40, 42, 48, 60, 80, 80, 96, 102, 126, 140, 140, 156, 156, 156, 174, 180, 180, 198, 216, 224, 224, 264, 276, 280, 294, 294, 300, 320, 340, 372, 380, 384, 440, 440, 468, 500, 504, 510, 528, 560, 582, 608, 616, 642, 680, 684, 690, 690, 696, 702, 736, 750
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OFFSET

1,1


LINKS

Table of n, a(n) for n=1..54.
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)=42.


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: A068544 A284174 A292982 * A129656 A048945 A111398
Adjacent sequences: A109794 A109795 A109796 * A109798 A109799 A109800


KEYWORD

nonn


AUTHOR

Walter Kehowski, Aug 15 2005


STATUS

approved



