A190992 Duplicate of A176035.

2, 1, 5, 6, 5, 6, 1, 8, 9, 10, 2, 3, 10, 2, 6, 8, 9, 13, 1, 5, 10, 13, 1, 4, 5, 6, 10, 12, 13, 14, 6, 11, 15, 18, 19, 1, 2, 8, 12, 13, 20, 21, 22, 1, 2, 11, 14, 15, 17, 22, 8, 9, 14, 16, 18, 25, 5, 6, 7, 9, 10, 13, 17, 18, 19, 21, 22, 23, 25, 1, 10, 12, 22, 24, 28, 29, 3, 6, 9, 11, 18, 22, 31, 2

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, Jun 02 2011

Keywords

• dead

Comments

Previous name was: Square excess of squarefree semiprimes.

Links

• G. C. Greubel, Table of n, a(n) for n = 1..5000

Programs

Magma

A006881:= [n: n in [1..1000] | EulerPhi(n) + DivisorSigma(1, n) eq 2*(n+1)];
[A006881[n] - Floor(Sqrt(A006881[n]))^2: n in [1..100]]; // G. C. Greubel, Oct 26 2022

Mathematica

A006881=Sort@Flatten@Table[Prime[m]*Prime[n],{n,2,150},{m,n-1}];
Table[A006881[[n]]-Floor[Sqrt[A006881[[n]]]]^2, {n,100}]

SageMath

A006881=[n for n in (1..750) if euler_phi(n) + sigma(n,1) == 2*n+2]
[A006881[n] - isqrt(A006881[n])^2 for n in range(101)] # G. C. Greubel, Oct 26 2022

Extensions

Data corrected by G. C. Greubel, Oct 26 2022

Marked as duplicate by R. J. Mathar, Aug 25 2025