OFFSET

1,3

COMMENTS

Concatenate of indices of distinct prime factors of n, in increasing order.

LINKS

FORMULA

a(prime(n)^k) = n for k > 0.

EXAMPLE

a(60) = a(2^2 * 3 * 5) = a(prime(1)^2 * prime(2) * prime(3)) = 123.

MATHEMATICA

a[n_] := FromDigits[Flatten@IntegerDigits@(PrimePi[#[[1]]] & /@ FactorInteger[n])]; Table[a[n], {n, 1, 70}]

CROSSREFS

KEYWORD

nonn,base

AUTHOR

Ilya Gutkovskiy, Nov 02 2019

STATUS

approved