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