A046433 Numbers such that 3 steps are needed to reach a prime under "Sum of digits raised to its digits' powers" procedure.

7, 26, 62, 126, 147, 148, 158, 162, 174, 184, 185, 206, 216, 248, 260, 261, 266, 284, 377, 399, 407, 408, 417, 418, 428, 470, 471, 480, 481, 482, 508, 518, 580, 581, 599, 602, 612, 620, 621, 626, 662, 704, 714, 737, 740, 741, 773, 804, 805, 814, 815, 824

Offset

1,1

Links

Marius A. Burtea, Table of n, a(n) for n = 1..5000

Example

26 -> 2^2 + 6^6 = 46660 -> 4^4 + 6^6 + 6^6 + 6^6 + 0^0 = 140225 -> 1^1 + 4^4 + 0^0 + 2^2 + 2^2 + 5^5 = 3391, which is prime, so 26 is a term.

Mathematica

sop[n_] := Total[#^# & /@ (IntegerDigits[n] /. {0 -> 1})]; Select[ Range[825], Boole /@ PrimeQ[Rest[NestList[sop, #, 3]]] == {0, 0, 1} &] (* Jayanta Basu, Jun 25 2013 *)

Prog

(Magma) f:=func<n| &+[a[i]^a[i]:i in [1..#a]] where a is Intseq(n) >; [k:k in [1..900] |not IsPrime(f(k)) and not IsPrime(f(f(k))) and IsPrime(f(f(f(k))))]; // Marius A. Burtea, Oct 27 2019

Crossrefs

Cf. A046431.

Sequence in context: A231888 A211645 A171340 * A128972 A135300 A024001

Adjacent sequences: A046430 A046431 A046432 * A046434 A046435 A046436

Keyword

nonn,base

Author

Patrick De Geest, Jul 15 1998

Status

approved