A371414 Euler phi function applied to the cubefull exponentially odd numbers (A335988).

1, 4, 18, 16, 100, 64, 72, 162, 294, 256, 288, 400, 1210, 648, 1024, 1458, 2028, 1176, 2500, 1800, 1152, 1600, 4624, 6498, 2592, 4096, 5292, 4840, 4704, 11638, 4608, 6400, 14406, 5832, 8112, 13122, 23548, 10000, 7200, 28830, 16200, 10368, 16384, 21780, 18496, 19360

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Formula

a(n) = A000010(A335988(n)).

Sum_{n>=1} 1/a(n) = Product_{p prime} (1 + 1/((p-1)^2*(p+1))) = zeta(2)^2 * Product_{p prime} (1 - 2/p^2 + 1/p^3 + 2/p^4) = 1.43921640806700099050... .

Mathematica

Join[{1}, EulerPhi /@ Select[Range[20000], AllTrue[Last /@ FactorInteger[#], #1 > 1 && OddQ[#1] &] &]]

Prog

(PARI) lista(max) = {my(f, ans); print1(1, ", "); for(k = 2, max, f = factor(k); ans = 1; for (i = 1, #f~, if (f[i, 2] == 1 || !(f[i, 2] % 2), ans = 0; break)); if(ans, print1(eulerphi(f), ", "))); }

Crossrefs

Cf. A000010, A098198, A335988.

Similar sequences: A323333, A371414, A371415.

Sequence in context: A070923 A064220 A205105 * A231957 A275952 A081420

Adjacent sequences: A371411 A371412 A371413 * A371415 A371416 A371417

Keyword

nonn,easy

Author

Amiram Eldar, Mar 22 2024

Status

approved