A358545 a(n) is the smallest number with exactly n divisors that are centered square numbers.

1, 5, 25, 325, 1625, 1105, 5525, 27625, 160225, 1022125, 801125, 5928325, 8491925, 29641625, 42459625, 444215525, 314201225, 2003613625, 1571006125, 14826740825, 12882250225, 127081657625, 64411251125, 88717383625

Offset

1,2

Comments

Any subsequent terms are > 10^10. - Lucas A. Brown, Dec 24 2022

Links

Table of n, a(n) for n=1..24.

Lucas A. Brown, Python program.

Eric Weisstein's World of Mathematics, Centered Square Number

Index entries for sequences related to divisors of numbers

Example

a(3) = 25 because 25 has 3 centered square divisors {1, 5, 25} and this is the smallest such number.

Prog

(PARI) iscsq(n) = issquare(2*n-1); \\ A001844
a(n) = my(k=1); while (sumdiv(k, d, iscsq(d)) != n, k++); k; \\ Michel Marcus, Nov 21 2022

Crossrefs

Cf. A001844, A005179, A130279, A300410, A358543, A358544.

Sequence in context: A370336 A145773 A197195 * A285602 A072324 A204544

Adjacent sequences: A358542 A358543 A358544 * A358546 A358547 A358548

Keyword

nonn,more

Author

Ilya Gutkovskiy, Nov 21 2022

Extensions

a(12)-a(15) from Michel Marcus, Nov 21 2022

a(16) from Martin Ehrenstein, Dec 02 2022

a(17)-a(24) from Jinyuan Wang, Dec 02 2022

Status

approved