cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A075460 Odd primitive numbers such that n! divided by product of factorials of all proper divisors of n is not an integer.

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%I A075460 #9 Aug 05 2017 12:52:13
%S A075460 1575,2835,3465,4095,5355,5775,5985,6435,6615,6825,7245,8085,9135,
%T A075460 9765,11655,12705,12915,13545,14805,15015,15435,16695,18585,19215,
%U A075460 19635,21105,21945,22275,22365,22995,23205,24885,25245,25935,26145,26565
%N A075460 Odd primitive numbers such that n! divided by product of factorials of all proper divisors of n is not an integer.
%C A075460 If a number is in the sequence, then all of its multiples would also meet the criterion, but are not included. This is meant by the word "primitive" in the definition.
%e A075460 1575 = 3^2*5^2*7 is in the sequence, because the product of the factorials of its proper divisors { 1, 3, 5, 7, 9, 15, 21, 25, 35, 45, 63, 75, 105, 175, 225, 315, 525 } does not divide 1575!. (For example, the former's 2-adic valuation equals 1588 while the latter's 2-adic valuation equals only 1569.) This is the smallest odd number with this property. - _M. F. Hasler_, Dec 30 2016
%t A075460 f[n_] := n!/Apply[Times, Drop[Divisors[n], -1]! ]; a = {}; Do[b = f[n]; If[ !IntegerQ[b], If[ Select[n/a, IntegerQ] == {}, Print[n]; a = Append[a, n]]], {n, 1, 28213, 2}]; a
%Y A075460 Cf. A075071. The first primitive n's with this property (most of which are even) are in A075422.
%K A075460 base,nonn
%O A075460 1,1
%A A075460 _Robert G. Wilson v_, Sep 16 2002
%E A075460 Edited by _M. F. Hasler_, Dec 30 2016