

A194099


Numbers m>=2, such that, if a prime p divides m^21, then every prime q<p divides m^21 as well.


1



3, 5, 7, 11, 17, 19, 29, 31, 41, 49, 71, 161, 251, 449, 769, 881, 1079, 1429, 3431, 4159, 4801, 6049, 8749, 19601, 24751, 246401, 388961, 1267111
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OFFSET

1,1


COMMENTS

No more terms <= 10^8.


LINKS



FORMULA



EXAMPLE

881^21 = 776160 = 2^5 * 3^2 * 5 *7^2 * 11 (all primes <= 11 appear), so 881 is a term.


MATHEMATICA

Select[Range[1, 10^4], First@ # == 1 && If[Length@ # > 1, Union@ Differences@ # == {1}, True] &@ PrimePi@ Map[First, FactorInteger[#^2  1]] &] (* Michael De Vlieger, Jul 02 2016 *)


PROG

(PARI) isok(n) = my(f = factor(n^21)); #f~ == primepi(f[#f~, 1]); \\ Michel Marcus, Jul 02 2016


CROSSREFS



KEYWORD

nonn,more


AUTHOR



STATUS

approved



