A355707 Nonsquare numbers k such that tau(sigma(tau(k))) = sigma(tau(sigma(k))), where tau is A000005 and sigma is A000203.

786432, 3500658, 41641938, 75031250, 121773618, 175781250, 408008178, 892531250, 1031215698

Offset

1,1

Comments

a(9) > 10^9.

From Jon E. Schoenfield, Jul 16 2022: (Start)

Additional terms < 10^12 (the lists below may not include all such terms):

- terms of the form 2*p^6*q^4, where p and q are distinct odd primes: 2610031250, 4984611858, 8745031250, 22102531250, 23178336818, 41404635378, 56789218098, 69194232018, 106837531250, 115908606338, 379290886578, 806279828978, 887445031250;

- terms of the form 2*p^10*q^2, where p and q are distinct odd primes: 5644531250, 32832031250, 67988281250, 98457031250, 154707031250, 199238281250, 335175781250, 544707031250, 584550781250. (End)

Links

Table of n, a(n) for n=1..9.

Prog

(PARI) isok(k) = !issquare(k) && (numdiv(sigma(numdiv(k))) == sigma(numdiv(sigma(k)))); \\ Michel Marcus, Jul 16 2022

Crossrefs

Cf. A000005, A000203, A076361.

Intersection of A000037 and A237613.

Sequence in context: A205261 A157993 A175747 * A115175 A104949 A237895

Adjacent sequences: A355704 A355705 A355706 * A355708 A355709 A355710

Keyword

nonn,more

Author

Mohammed Yaseen, Jul 14 2022

Extensions

a(9) from Jon E. Schoenfield, Jul 16 2022

Status

approved