A059992 Numbers with an increasing number of nonprime divisors.

1, 4, 8, 12, 24, 36, 48, 60, 72, 120, 180, 240, 360, 720, 840, 1080, 1260, 1440, 1680, 2160, 2520, 4320, 5040, 7560, 10080, 15120, 20160, 25200, 27720, 30240, 45360, 50400, 55440, 75600, 83160, 110880, 151200, 166320, 221760, 277200, 332640

Offset

1,2

Comments

Positions of records in A033273.

Links

Amiram Eldar, Table of n, a(n) for n = 1..571 (terms 1..146 from Ray Chandler)

Example

a(4)=12 because twelve has 4 nonprime divisors {1, 4, 6 and 12} whereas a(3)=8 has only 3; and twelve is the first number greater than eight which exhibits this property.

Mathematica

l = 0; Do[ c = Count[PrimeQ[ Divisors[n] ], False]; If[c > l, l = c; Print[n] ], {n, 1, 10^6} ]

Prog

(PARI) lista(nn) = {my(m=0, nb); for (n=1, nn, nb = sumdiv(n, d, !isprime(d)); if (nb > m, m = nb; print1(n, ", ")); ); } \\ Michel Marcus, Jul 16 2019

Crossrefs

Cf. A055079, A002182, A033273, A180040.

Sequence in context: A272708 A157416 A278602 * A050570 A335992 A233341

Adjacent sequences: A059989 A059990 A059991 * A059993 A059994 A059995

Keyword

nonn

Author

Robert G. Wilson v, Mar 08 2001

Extensions

Alternate description and b-file from Ray Chandler, Aug 07 2010

Status

approved