A121614 - OEIS

%I #9 Feb 13 2021 01:08:47

%S 27,45,54,72,78,87,126,159,162,168,186,195,207,216,234,243,249,261,

%T 267,270,276,294,324,342,348,357,375,384,405,423,429,432,438,450,483,

%U 492,504,519,537,540,573,591,612,618,621,627,672,678,681,687,702,708,720

%N Numbers that have composite sum of digits and prime sum of squares of digits.

%H Vincenzo Librandi, <a href="/A121614/b121614.txt">Table of n, a(n) for n = 1..1000</a>

%e For example: the sum of digits of 27 is 9 which is composite; the sum of squares of digits of 27 is 53 which is prime.

%t sod[k_, m_] := Plus @@ (IntegerDigits[k]^m); Select[ Table[n, {n, 1000}], (! PrimeQ[sod[ #, 1]] && PrimeQ[sod[ #, 2]]) &]

%Y Cf. A091362 (Primes p such that the sum of the digits of p is not prime, but the sum of the squares of the digits of p is prime) is a prime subsequence of this sequence.

%K base,nonn

%O 1,1

%A _Tanya Khovanova_, Sep 08 2006