A341634 - OEIS

A341634

Smallest prime whose product of digits (A007954) is the n-th 7-smooth number = A002473(n), with a(0) = 101.

101, 11, 2, 3, 41, 5, 23, 7, 181, 19, 251, 43, 127, 53, 281, 29, 541, 37, 83, 11551, 139, 47, 523, 1481, 157, 149, 12451, 67, 59, 283, 11177, 2551, 239, 1187, 1453, 79, 881, 257, 89, 1553, 2851, 199, 347, 563, 1483, 277, 14551, 1753, 269, 827, 853, 15551, 367

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OFFSET

0,1

COMMENTS

For n>=1, equals A107698 without the zeros.

101 is the smallest prime with the digit 0, so A007954(101) = 0 but as 0 is not a 7-smooth number, it is chosen a(0) = 101.

LINKS

Robert Israel, Table of n, a(n) for n = 0..645

FORMULA

a(n) = A107698(A002473(n)) for n>=1. - Amiram Eldar, Feb 17 2021

EXAMPLE

83 is prime, A007954(83) = 8*3 = 24 that is the 18th 7-smooth number, and as no prime < 83 has a product of digits = 24, a(18) = 83.

MATHEMATICA

pod[n_] := Times @@ IntegerDigits[n]; seq[max_] := Module[{sm7 = Join[{0}, Select[Range[max], Max[FactorInteger[#][[;; , 1]]] <= 7 &]], m, s, n, c, i, ind}, m = Length[sm7]; s = Table[0, {m}]; n = 1; c = 0; While[c < m, n = NextPrime[n]; i = pod[n]; If[MemberQ[sm7, i], ind = Position[sm7, i][[1, 1]]]; If[s[[ind]] == 0, c++; s[[ind]] = n]]; s]; seq[150] (* Amiram Eldar, Feb 16 2021 *)

CROSSREFS

Cf. A002473, A004954, A007954, A053666, A107698, A335331.

Sequence in context: A282222 A282199 A266460 * A060386 A062584 A085054

Adjacent sequences: A341631 A341632 A341633 * A341635 A341636 A341637

KEYWORD

nonn,base

AUTHOR

Bernard Schott, Feb 16 2021

EXTENSIONS

More terms from Amiram Eldar, Feb 16 2021

STATUS

approved