A121614 Numbers that have composite sum of digits and prime sum of squares of digits.

27, 45, 54, 72, 78, 87, 126, 159, 162, 168, 186, 195, 207, 216, 234, 243, 249, 261, 267, 270, 276, 294, 324, 342, 348, 357, 375, 384, 405, 423, 429, 432, 438, 450, 483, 492, 504, 519, 537, 540, 573, 591, 612, 618, 621, 627, 672, 678, 681, 687, 702, 708, 720

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Example

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.

Mathematica

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

Crossrefs

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.

Sequence in context: A357077 A259504 A307373 * A046340 A046316 A046373

Adjacent sequences: A121611 A121612 A121613 * A121615 A121616 A121617

Keyword

base,nonn

Author

Tanya Khovanova, Sep 08 2006

Status

approved