A122065 Take sum of squares of digits of previous term; start with 74169.

74169, 183, 74, 65, 61, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4

Offset: 1

Author

Herman Jamke (hermanjamke(AT)fastmail.fm), Sep 14 2006

Keywords

• nonn
• base
• easy

Comments

From a quiz, cf. Russel & Carter reference.

References

• K. Russell and P. Carter, Number Puzzles, W. Foulsham and Co. Ltd. (1993).

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..100
• Index entries for linear recurrences with constant coefficients, signature (0, 0, 0, 0, 0, 0, 0, 1).

Crossrefs

Cf. A000216 (main entry for related sequences), A003132 (the iterated "sum digits squared" map).

Programs

Magma

[74169, 183, 74, 65, 61] cat &cat[[37, 58, 89, 145, 42, 20, 4, 16]: n in [0..17]]; // Vincenzo Librandi, Jan 29 2013

Mathematica

NestList[Total[IntegerDigits[#]^2]&, 74169, 80] (* Vincenzo Librandi, Jan 29 2013 *)

PARI

A122065_vec=vector(50,n,t=if(n>1,norml2(digits(t)),74169));
A122065(n)=A122065_vec[n%8+(n>7)*8] \\ M. F. Hasler, Apr 27 2018

Formula

a(n) = A000218(n) for n >= 4, a(n) = A000216(n-2) for n >= 6. - M. F. Hasler, Apr 27 2018