A338842 No even digit is present in a(n) * a(n+1).

1, 3, 5, 7, 11, 9, 13, 15, 21, 17, 23, 25, 31, 43, 37, 27, 19, 29, 33, 35, 45, 39, 41, 77, 49, 73, 81, 71, 47, 79, 65, 51, 61, 55, 57, 63, 53, 67, 59, 87, 85, 91, 83, 93, 101, 75, 69, 113, 141, 95, 105, 127, 119, 129, 133, 135, 117, 147, 213, 149, 115, 97, 103, 151, 209, 153, 235, 169, 233, 143, 137, 229

Offset

1,2

Comments

This is the lexicographically earliest sequence of distinct positive terms with this property.

Links

Carole Dubois, Table of n, a(n) for n = 1..5000

Example

a(1) * a(2) = 1 * 3 = 3 (no even digit is present);
a(2) * a(3) = 3 * 5 = 15 (no even digit is present);
a(3) * a(4) = 5 * 7 = 35 (no even digit is present); etc.

Mathematica

Block[{a = {1}}, Do[Block[{k = 3}, While[Nand[FreeQ[a, k], NoneTrue[IntegerDigits@ Total[a[[-1]]*k], EvenQ]], k += 2]; AppendTo[a, k]], {i, 2, 72}]; a] (* Michael De Vlieger, Nov 12 2020 *)

Crossrefs

Cf. A014261 (no even digits).

Cf. A338839, A338840, A338841, A338843, A338844, A338845, A338846 (variants on the same idea).

Sequence in context: A235379 A174839 A245462 * A022457 A066066 A241957

Adjacent sequences: A338839 A338840 A338841 * A338843 A338844 A338845

Keyword

nonn,base,look

Author

Eric Angelini and Carole Dubois, Nov 11 2020

Status

approved