A272553 Numbers n whose sum of divisors equals the sum of divisors of 2n+1.
20, 464, 650, 2744, 3980, 5504, 5736, 5922, 7032, 8130, 10472, 18618, 24312, 27654, 38874, 39500, 43032, 45492, 56870, 64410, 71058, 79068, 85158, 89178, 92130, 97014, 109928, 117114, 118902, 127688, 130304, 175554, 180438, 187304, 188292, 208452, 224058, 244674, 249788, 269192, 294380, 305624, 347964
Offset: 1
Keywords
Examples
20 is a term as its sum of divisors, 42=1+2+4+5+10+20, is the same as the sum of divisors of 41=2*20+1; 41 has only two divisors 1 and 41.
Links
- Giovanni Resta, Table of n, a(n) for n = 1..1000
Crossrefs
Programs
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Maple
select(t -> numtheory:-sigma(t) = numtheory:-sigma(2*t+1), [$1..10^6]); # Robert Israel, May 03 2016
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Mathematica
Select[Range@500000, DivisorSigma[1, #]==DivisorSigma[1, 2*#+1]&]
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PARI
for (n=1, 500000, (sigma(n)==sigma(2*n+1)) && print1(n ", "))
Comments