A372335 - OEIS

A372335

For a positive number k, let L(k) denote the list consisting of k followed by the prime factors of k, with repetition, in nondecreasing order; sequence gives composite k such that the digits of L(k) alternate being larger than and then smaller than the previous digit.

14, 15, 78, 161, 591, 1214, 1317, 1318, 1326, 1407, 1418, 1438, 1506, 1509, 1514, 1527, 1538, 1618, 1626, 1646, 1658, 1703, 1714, 1718, 1734, 1739, 1758, 1814, 1834, 1838, 1839, 1857, 1858, 1934, 1938, 2307, 2427, 2509, 2517, 2534, 2535, 2715, 2757, 2758, 2869, 2958, 3419, 3439, 3514, 3523

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

No term can end in 0 or 2; a number ending in 2 would mean the first prime factor is 2, which would disqualify the number, while a number ending in 0 would mean the first 3 distinct prime factors would have to be 2, 3, 5 or 2, 5, either of which would also disqualify the number.

LINKS

Scott R. Shannon, Table of n, a(n) for n = 1..10000

EXAMPLE

161 is a term as 161 = 7 * 23 which when concatenated give "161723", the digits of which alternate from being larger than and then smaller than the previous digit.

CROSSREFS

Cf. A372336, A372280, A372308, A372034, A372029, A056704.

Sequence in context: A041408 A041406 A041410 * A041412 A041414 A033050

Adjacent sequences: A372332 A372333 A372334 * A372336 A372337 A372338

KEYWORD

nonn,base

AUTHOR

Scott R. Shannon, Apr 28 2024

STATUS

approved