A115661 Numbers k which have the same number of distinct prime divisors as the reverse of k.

1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 15, 16, 17, 21, 22, 23, 26, 28, 31, 32, 33, 36, 37, 39, 44, 45, 51, 54, 55, 56, 57, 58, 61, 62, 63, 65, 66, 68, 69, 71, 73, 75, 77, 79, 82, 85, 86, 88, 93, 96, 97, 99, 101, 107, 108, 111, 113, 115, 116, 117, 121, 122, 123, 125, 128

Offset

1,2

Links

G. C. Greubel, Table of n, a(n) for n = 1..1000

Example

omega(16) = omega(61) = 1.

Mathematica

Select[Range[130], PrimeNu[#]==PrimeNu[FromDigits[Reverse[ IntegerDigits[ #]]]]&] (* Harvey P. Dale, Jan 14 2012 *)

Prog

(Python)
from sympy import factorint
def ok(n): return len(factorint(n)) == len(factorint(int(str(n)[::-1])))
print([k for k in range(1, 129) if ok(k)]) # Michael S. Branicky, Mar 05 2026

Crossrefs

Cf. A001221, A115662.

Sequence in context: A394676 A395790 A133812 * A318735 A002244 A037173

Adjacent sequences: A115658 A115659 A115660 * A115662 A115663 A115664

Keyword

base,nonn

Author

Giovanni Resta, Jan 29 2006

Status

approved