A390120 Integers k that can be represented by at least one concatenation (x, y, z) such that k = A000203(x)*A000203(y)*A000203(z).

576, 4536, 16926, 93184, 217854, 331776, 1536192, 1737216, 2025540, 2536920, 3273600, 11249280, 14929920, 15091664, 17563392, 25819668, 29393280, 29730240, 32890752, 53157312, 57097152, 93562560, 122135040, 128733696, 151683840, 163708272, 211559040, 212486400

Offset

1,1

Links

Paolo P. Lava, Table of n, a(n) for n = 1..52

Paolo P. Lava, List of k, x, y, z

Example

a(7) = 1536192 = A000203(15)*A000203(361)*A000203(92) = 24*381*168;
a(10) = 2536920 = A000203(2)*A000203(53)*A000203(6920) = 3*54*15660.
540 is not in the sequence as 540 = A000203(5) * A000203(40) = 6*90 but it's the product of a tuple of size two instead of size three. - David A. Corneth, Jan 30 2026

Prog

(PARI) is(n) = {targetprod = n; found = 0; process(n, n, 0); found}
process(nprod, nconcat, qprod) = {if(nconcat == 0 && nprod == 1 && qprod == 3, found = 1); if(found == 1, return); if(qprod >= 3, return); my(d = digits(nconcat), c); for(i = 1, #d, c = nconcat%10^i; if(c == 0, next); sc = sigma(c); if(nprod % sc == 0, process(nprod \ sc, nconcat\10^i, qprod + 1)))} \\ David A. Corneth, Jan 30 2026

Crossrefs

Cf. A000203, A253824.

Sequence in context: A067225 A325475 A268797 * A036514 A269034 A188787

Adjacent sequences: A390117 A390118 A390119 * A390121 A390122 A390123

Keyword

nonn,base

Author

Paolo P. Lava, Jan 18 2026

Extensions

a(23) onward by Giovanni Resta, Jan 28 2026

Status

approved