

A330434


a(1) = 1, a(2) = 2; thereafter a(n) = smallest number not occurring earlier such that the sum of three successive digits is prime.


1



1, 2, 4, 5, 8, 6, 3, 20, 9, 22, 7, 24, 10, 11, 13, 17, 31, 15, 51, 19, 35, 33, 53, 37, 39, 55, 71, 57, 73, 77, 91, 75, 59, 95, 93, 79, 110, 12, 21, 28, 14, 25, 42, 18, 23, 26, 32, 27, 40, 16, 41, 60, 50, 29, 62, 30, 43, 44, 34, 45, 48, 54, 49, 46, 38, 63, 80, 52, 47, 64, 36, 83, 68, 56, 61, 66, 58, 65, 84, 70, 67, 401
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OFFSET

1,2


LINKS



EXAMPLE

After 8 and 6 the next term is 3 as 8+6+3 = 17 is a prime;
After 6 and 3 the next term is 20 as 6+3+2 = 11 and 3+2+0 = 5 are primes;
After 20 the next term is 9 as 2+0+9 = 11 is a prime; etc.


MATHEMATICA

Nest[Append[#, Block[{k = 3}, While[Nand[FreeQ[#, k], AllTrue[Table[Total@ #[[i ;; i + 2]], {i, Length@ #  2}], PrimeQ] &@ Flatten@ IntegerDigits@ Append[#, k] ], k++]; k]] &, {1, 2}, 80] (* Michael De Vlieger, Dec 14 2019 *)


CROSSREFS

Cf. A076990 (3 successive terms have a prime sum), A330424 (3 successive terms AND 3 successive digits have a prime sum).


KEYWORD

base,nonn


AUTHOR



STATUS

approved



