

A269850


a(n) = number of integers k <= n for which prime(k+1)prime(k) is a multiple of three.


5



0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 2, 2, 3, 4, 4, 5, 5, 5, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 9, 10, 10, 11, 12, 12, 12, 12, 12, 12, 13, 14, 14, 14, 14, 15, 15, 15, 16, 17, 18, 18, 19, 19, 19, 19, 19, 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 22, 23, 23, 24, 24, 24, 24, 24, 24, 24, 24, 25, 25, 26, 26, 26, 26, 26, 27
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OFFSET

1,11


COMMENTS

a(n) = number of terms of A270190 <= n, the least monotonic left inverse of A270190.


LINKS



FORMULA

Other identities. For all n >= 1:


MATHEMATICA

Table[Count[Select[Range@ 125, Divisible[Prime[# + 1]  Prime@ #, 3] &], k_ /; k <= n], {n, 91}] (* Michael De Vlieger, Mar 17 2016 *)


PROG

(PARI) a(n) = sum(k=1, n, ((prime(k+1)  prime(k)) % 3) == 0); \\ Michel Marcus, Mar 18 2016


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



