Bounding my Erdös number
From the definition
of the Erdös number, to establish a bound of 4 for mine, it suffices to
supply the following citations.

Anderson, J.M., Erdös, P., Pinkus, A, Shisha, Oved,
The closed linear span of $\{x^kc_k\}_1^{\infty}$.
J. Approx. Theory 43 (1985), pp. 7580.

Pinkus, A, Braess, D,
Interpolation by Ridge Functions,
J. Approx. Theory 73 (1993), pp. 218236

Braess, D, C. Schwab,
Approximation on simplices with respect to weighted Sobolev norms.
J. Approx. Theory 103 (2001), No. 2, 329337.
 J.M. Melenk, C. Schwab,
Analytic regularity for a singularly perturbed problem,
SIAM J. Math. Anal. 30 (1999), 379400