A327920 - OEIS

%I #10 May 24 2022 19:20:10

%S 23,53,73,113,173,193,233,293,313,37,137,197,317,211,311,2311

%N The 16 pure prime dates of each year of the form concatenate(day,month) with month and day also prime numbers.

%C For the case of the 16, respectively 17, pure prime dates of the form concatenate(month,day) see A327918 (non-leap years) and A327919 (leap years).

%C Only the three months m = 3, 7, and 11 qualify. The qualifying days are for November (m = 11): d = 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, and for months March and July (m = 3 and 7): d = 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31.

%C The months m = 3, 7, 11 contribute 9, 4, 3 dates, respectively, adding to 16.

%t Select[Flatten[Table[d*10^IntegerLength[m]+m,{m,{3,7,11}},{d,Prime[ Range[ 11]]}]],PrimeQ] (* _Harvey P. Dale_, May 24 2022 *)

%Y Cf. A055782 (first nine terms), A055783 (first four terms), A114007 (three terms starting with n = 8). A327346 (with d and m also nonprime allowed), A327918, A327919.

%K nonn,easy,fini,full

%O 1,1

%A _Wolfdieter Lang_, Oct 08 2019