A206026 a(n) = smallest number m such that sigma(k) = m has at least n positive solutions k.

1, 12, 24, 72, 72, 168, 240, 336, 360, 504, 576, 720, 720, 720, 720, 1440, 1440, 1440, 1440, 1440, 1440, 2880, 2880, 2880, 2880, 2880, 2880, 2880, 2880, 4320, 4320, 4320, 4320, 4320, 4320, 5760, 5760, 8640, 8640, 8640, 8640, 8640, 8640, 8640, 8640, 8640, 8640

Offset

1,2

Comments

Sequence of numbers from A145899.

Links

Amiram Eldar, Table of n, a(n) for n = 1..1000

Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).

Example

a(6) = 168 because 168 is the smallest value of sigma(k) for n = 6 positive integers k such that sigma(k) = 168 has solution; k = 60, 78, 92, 123, 143, 167.

Prog

(PARI) list(len) = {my(v = vector(len), k = 1, c = 0, i); while(c < len, i = invsigmaNum(k); for(j = 1, i, if(j <= len && v[j] == 0, v[j] = k; c++)); k++); v; } \\ Amiram Eldar, Dec 15 2024, using Max Alekseyev's invphi.gp

Crossrefs

Cf. A000203, A054973, A085790, A145899, A206027.

Sequence in context: A332037 A332039 A001335 * A145899 A172011 A239635

Adjacent sequences: A206023 A206024 A206025 * A206027 A206028 A206029

Keyword

nonn

Author

Jaroslav Krizek, Feb 03 2012

Status

approved