A176035 Difference between product of two distinct primes and previous perfect square.
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
Offset: 1
Links
- G. C. Greubel, Table of n, a(n) for n = 1..5000
Programs
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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
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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}] (* Vladimir Joseph Stephan Orlovsky, Jun 02 2011 *)
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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
Comments