1,1

a(n) is also the difference between the n-th perfect number and its number of proper divisors.

a(n) = A152770(A000396(n)) = A000396(n)-A133033(n).

a(2) is 23 because the second perfect number is 28 and the sum of proper divisors of 28 is also 28 = 1+2+4+7+14 and the number of proper divisors of 28 is 5, then 28-5 = 23.

Cf. A000396, A001065, A032741, A133033, A152770.

Sequence in context: A055326 A133338 A116986 this_sequence A134050 A101191 A127900

Adjacent sequences: A154893 A154894 A154895 this_sequence A154897 A154898 A154899

more,nonn

Omar E. Pol (info(AT)polprimos.com), Jan 25 2009